FOR PUBLICATION
  UNITED STATES COURT OF APPEALS
       FOR THE NINTH CIRCUIT

KINGMAN REEF ATOLL INVESTMENTS,         
L.L.C.,
                 Plaintiff-Appellant,
                 v.
UNITED STATES OF AMERICA;                     No. 07-16817
UNITED STATES DEPARTMENT OF THE
INTERIOR; GALE A. NORTON,                      D.C. No.
                                            CV-05-00151-JMS
Secretary of the Interior; UNITED
                                               OPINION
STATES FISH AND WILDLIFE SERVICE;
STEVEN A. WILLIAMS, in his official
capacity as Director of the US
Fish & Wildlife Service,
              Defendants-Appellees.
                                        
        Appeal from the United States District Court
                 for the District of Hawaii
       J. Michael Seabright, District Judge, Presiding

                  Argued and Submitted
             June 20, 2008—Honolulu, Hawaii

                  Filed September 4, 2008

    Before: Alfred T. Goodwin, Pamela Ann Rymer, and
              Sandra S. Ikuta, Circuit Judges.

                   Opinion by Judge Ikuta




                            12201
               KINGMAN REEF v. UNITED STATES           12205


                        COUNSEL

Therese Y. Cannata (argued), Michael M. Ching, and Carolyn
A. Johnston of Cannata, Ching & O’Toole LLP, San Fran-
cisco, California, Christian P. Porter and Donna H. Yama-
moto of Brooks Tom Porter & Quitquit LLP, Honolulu,
Hawaii, and Jon M. Van Dyke, Honolulu, Hawaii, for the
plaintiff-appellant.

Allen M. Brabender (argued), David C. Shilton, and Donna
Fitzgerald, Attorneys, Environmental and Natural Resources
Division, United States Department of Justice, and Ronald J.
Tenpas, Assistant Attorney General, for the defendants-
appellees.


                         OPINION

IKUTA, Circuit Judge:

  Kingman Reef Atoll Investments, LLC (KRAI), filed this
action against various United States departments and officers
12206            KINGMAN REEF v. UNITED STATES
in their official capacities (collectively, the “United States”),
pursuant to the Quiet Title Act (QTA), 28 U.S.C. § 2409a.
KRAI seeks to quiet title to Kingman Reef, a small, low-lying
coral reef atoll located approximately 930 miles south of
Honolulu, Hawaii. The district court dismissed KRAI’s claim
for lack of subject matter jurisdiction. We affirm, because
KRAI’s predecessor knew or should have known of the claim
of the United States more than twelve years prior to KRAI’s
filing of the complaint in this case, and KRAI has failed to
demonstrate that the United States has clearly and unequivo-
cally abandoned its claim of interest in Kingman Reef.

                                 I

   “Kingman Reef is a low-lying, coral reef atoll comprised of
small emergent land spits and partially exposed coral reefs
that surround a deep central lagoon, located approximately
930 miles south of Honolulu, Hawaii.” Kingman Reef Atoll
Invs., L.L.C. v. United States, 

, 1105 (D.
Haw. 2007). Kingman Reef’s only dry land consists of coral
rubble and marine shells sitting less than two meters above
sea level at its highest point, making it unfit for human habita-
tion. See 

reported Western contact at Kingman Reef was by
an American whaler in 1798; eponymous Captain W.E. King-
man later visited the reef in 1853. 

Guano Com-
pany claimed the reef in 1860, although there is no evidence
that guano existed or was ever mined there.

  KRAI’s interest in Kingman Reef dates to 1922, when an
employee of the Island of Palmyra Copra Company claimed
Kingman Reef in the name of the United States for his
employer to use as a fishing base. 

Copra
Company purported to cede Kingman Reef to the Fullard-Leo
family that same year.1 On October 5, 1932, a member of the
  1
  The Fullard-Leo family transferred its interest in Kingman Reef to
KRAI on November 17, 2000.
                  KINGMAN REEF v. UNITED STATES                  12207
Fullard-Leo family approached United States officials in
Oahu to inquire whether he could sell various islands includ-
ing Kingman Reef to foreign buyers and whether the United
States wished to purchase the islands instead. Thereafter, the
United States, by the Navy and State Department, began to
investigate whether Kingman Reef was a sovereign territory
of the United States and, if so, whether it was owned by the
United States or by the Fullard-Leo family. By a memoran-
dum of November 7, 1934, a legal advisor of the State
Department advised that “it might be well for this Govern-
ment to take some affirmative action to show definitely that
[Kingman Reef] is a part of the territory of the United States.
The mere mention of it in an Act of Congress as American
territory would be sufficient.”

  President Roosevelt issued Executive Order 6935 on
December 29, 1934. Kingman 

.
The order states:

      By virtue of and pursuant to the authority vested in
      me by the act of June 25, 1910 [the Pickett Act], and
      as President of the United States, it is ordered that
      . . . Kingman Reef . . . [is] hereby, reserved, set
      aside, and placed under the control and jurisdiction
      of the Secretary of the Navy for administrative pur-
      poses . . . . This order shall continue in full force and
      effect unless and until revoked by the President or by
      act of Congress.

Exec. Order No. 6935. The Pickett Act, referenced in the
order, permitted the President, “at any time in his discretion,
[to] temporarily withdraw from settlement, location, sale, or
entry any of the public lands of the United States . . . and
reserve the same for . . . public purposes to be specified in the
orders of withdrawals.” Pickett Act of June 25, 1910, Ch. 421,
36 Stat. 847.2
  2
   Although the Pickett Act has been repealed, all withdrawals effected
under the act “remain in full force and effect until modified” under the
12208             KINGMAN REEF v. UNITED STATES
   Following President Roosevelt’s issuance of Executive
Order No. 6935 in 1934, Leslie and Ellen Fullard-Leo wrote
to Samuel Wilder King, who was then serving in the United
States House of Representatives as a delegate from the terri-
tory of Hawaii. In their April 20, 1937 letter, the Fullard-Leos
acknowledged that Kingman Reef’s “ownership presumably
rests with the State or Navy Department,” and requested com-
pensation only for the cost of sending their boat to Kingman
Reef “together with taxes and accrued interest over a period
of fifteen years.” Samuel Wilder King forwarded this request
to Claude A. Swanson, Secretary of the Navy, who replied in
a letter dated May 29, 1937 that “[t]he records of the Navy
Department do not indicate that there were any vested rights
on Kingman Reef in favor of private interests on the date of
the issuance of th[e] Executive Order [6935].” On March 29,
1938, attorneys representing the Fullard-Leos sent a letter to
Secretary Swanson, acknowledging the Navy’s position that
the family did not own Kingman Reef, and threatening legal
action to establish such ownership. See Kingman Reef, 545 F.
Supp. 2d at 1107. By letter of April 26, 1938, G. J. Rowcliff,
the Judge Advocate General of the Navy, rebuffed the fami-
ly’s claim of ownership over Kingman Reef. Rowcliff stated:

      It will be noted that the island, including its reefs and
      tide and submerged lands, was under the control and
      jurisdiction of the United States long before the
      claim of Mrs. Fullard-Leo arose, and by Executive
      Order No. 6935, dated December 29, 1934, it was
      placed under the control and jurisdiction of the Navy
      Department. Under the circumstances, the showing
      made is not sufficient to uphold the claim of Mrs.
      Fullard-Leo.

Policy and Management Act of 1976 or some other law. See
Pub. L. No. 94-579 §§ 701(c), 704(a), 90 Stat. 2743, 2786, 2792; Kingman

.
                KINGMAN REEF v. UNITED STATES             12209
   On February 14, 1941, President Roosevelt issued another
executive order establishing a “Kingman Reef Naval Defen-
sive Sea Area.” Exec. Order No. 8682, amended by Exec.
Order 8729. This Executive Order established that “[a]t no
time shall any person, other than persons on public vessels of
the United States, enter [the Kingman Reef area],” and dele-
gated enforcement of the order to the Secretary of the Navy.

subsequently promulgated regulations restrict-
ing access to Kingman Reef. See 32 C.F.R. § 761.3(a)(2)(v),
(b)(2).

   In the fifty years after World War II, both the United States
Navy and representatives of the Fullard-Leo family purported
to grant third party requests to visit or fish at Kingman Reef.
See Kingman 

. For example,
KRAI submitted a declaration from a private citizen stating
his impression that “the community of sailors and fishermen
in Honolulu . . . . knew that . . . Kingman Reef belonged to
the Fullard-Leo family because of the way they took care of
[it] and protected [it] at their expense,” and that only the
Fullard-Leo family could grant permission to travel to and
fish at Kingman Reef. The record contains several other dec-
larations of similar import.

   At the same time, the Navy also asserted its authority to
grant access to Kingman Reef. A July 27, 1973 letter from
Senator Hiram Fong, and a Navy memorandum of August 2,
1973, both in response to the request of a private citizen seek-
ing “permission to fish on and about Kingman Reef,” indicate
that permission to travel to and fish at Kingman Reef could
be granted only by the Navy.

   The issue of rightful ownership of Kingman Reef came into
greater focus in the 1990s, when the United States Fish and
Wildlife Service (an agency within the Department of the
Interior) began to consider acquiring Kingman Reef and
nearby Palmyra Atoll (owned by the Fullard-Leo family) for
the purpose of establishing a National Wildlife Refuge. See
12210              KINGMAN REEF v. UNITED STATES

The Fish and Wildlife Service’s preliminary
investigations into acquiring the reef indicated its initial
understanding that the Fullard-Leos owned the reef. For
example, an internal Fish and Wildlife Service document
from August 1997 states:

      Kingman Reef was annexed on behalf of the United
      States in 1922, by the Palmyra Copra Company
      (Fullard-Leo Family), and the family claims owner-
      ship. It is an unincorporated U.S. possession admin-
      istered by the U.S. Department of the Navy. The
      Service is proposing to study fee title acquisition of
      Kingman Reef from the center of the atoll to the 3-
      nautical mile limit.

Consistent with this understanding, Fish and Wildlife Service
employees obtained the Fullard-Leos’ permission to access
the reef, and signed indemnity and waiver agreements
requested by the Fullard-Leo family. However, an August 6,
1998 confidential internal memorandum from a high-ranking
Department of the Interior staff member to the Secretary indi-
cated uncertainty as to who owned Kingman Reef. The mem-
orandum noted that “[t]he owners of Palmyra also claim
ownership of Kingman Reef, but the United States disputes
this claim,” and raised the possibility that the Department of
the Interior could obtain ownership over Kingman Reef
through “an agreement [to transfer the island from] the
Department of Defense.”3 On August 25, 2000, the Fish and
  3
    In addition to these communications from the Department of Interior,
KRAI notes several other documents indicating various government
employees’ understanding that the Fullard-Leos claimed ownership to
Kingman Reef. For example, a letter dated August 12, 1997, from a Con-
gressional staffer to the House Resources Committee to an agent of the
Fullard-Leos, thanked the agent for “sending the information clarifying the
rightful title of the Fullard-Leo’s [sic] to Palmyra and Kingman Reef” and
stated that “[t]he brief is well documented regarding the basis for clear
title to the entire area of Palmyra and Kingman, including surrounding
reefs.” In addition, the General Counsel of National Oceanic and Atmo-
                   KINGMAN REEF v. UNITED STATES                    12211
Wildlife Service obtained control and jurisdiction over King-
man Reef through a no-cost transfer from the Department of
the Navy. The Secretary of the Interior established the King-
man Reef National Wildlife Refuge on January 18, 2001. See
Kingman 

.

   On March 4, 2005, KRAI brought this action to quiet title
to Kingman Reef under 28 U.S.C. § 2409a. On June 4, 2007,
the United States filed a motion for dismissal for lack of sub-
ject matter jurisdiction and for failure to state a claim, Fed. R.
Civ. P. 12(b)(1), (6), and for summary judgment. Fed. R. Civ.
P. 56. Holding that the action was untimely under the twelve-
year limitations period established by 28 U.S.C. § 2409a(g),
the district court dismissed the complaint for lack of subject
matter jurisdiction pursuant to Fed. R. Civ. P. 12(b)(1). This
appeal followed.

                                    II

   The question whether subject matter jurisdiction exists is
one of law that we review de novo. United States v. Peninsula
Commc’ns, Inc., 

, 836 (9th Cir. 2002). Unless
the jurisdictional issue is inextricable from the merits of a
case, the court may determine jurisdiction on a motion to dis-
miss for lack of jurisdiction under Rule 12(b)(1) of the Fed-
eral Rules of Civil Procedure. Roberts v. Corrothers, 

, 1177 (9th Cir. 1987). Under Rule 12(b)(1):

     the district court is free to hear evidence regarding
     jurisdiction and to rule on that issue prior to trial,
     resolving factual disputes where necessary. In such

spheric Administration indicated in a letter dated October 17, 1997 to the
Executive Director of the Western Pacific Regional Fishery Management
Council (in the context of discussing the jurisdiction of the Department of
the Interior over commercial bottom fishing activities) that the Fullard-
Leo family owned Kingman Reef.
12212           KINGMAN REEF v. UNITED STATES
    circumstances, no presumptive truthfulness attaches
    to plaintiff’s allegations, and the existence of dis-
    puted material facts will not preclude the trial court
    from evaluating for itself the merits of jurisdictional
    claims.

marks and alterations omitted). A dis-
trict court’s findings of fact relevant to its determination of
subject matter jurisdiction are reviewed for clear error. Penin-
sula 

. When “the accrual of the
statute of limitations in part turns on what a reasonable person
should have known, we review this mixed question of law and
fact for clear error.” Rose v. United States, 

,
1259 (9th Cir. 1990); see also Shultz v. Dep’t of Army, 

, 1159 (9th Cir. 1989). Because estoppel is an equi-
table concept requiring the exercise of the district court’s dis-
cretion, we review “the district court’s rejection of appellants’
equitable estoppel argument under the abuse of discretion
standard.” Hoefler v. Babbitt, 

, 727 (9th Cir.
1998).

                              III

   [1] The Quiet Title Act of 1972, 28 U.S.C. § 2409a, waives
the federal government’s sovereign immunity to certain civil
actions by plaintiffs seeking to quiet title to property in which
the United States claims an interest. Section 2409a(a) pro-
vides, in pertinent part:

    The United States may be named as a party defen-
    dant in a civil action under this section to adjudicate
    a disputed title to real property in which the United
    States claims an interest, other than a security inter-
    est or water rights.

   [2] The QTA’s waiver of sovereign immunity is subject to
numerous exceptions and restrictions, including a statute of
limitations. Section 2409a(g) provides:
                KINGMAN REEF v. UNITED STATES              12213
    Any civil action under this section, except for an
    action brought by a State, shall be barred unless it is
    commenced within twelve years of the date upon
    which it accrued. Such action shall be deemed to
    have accrued on the date the plaintiff or his pre-
    decessor in interest knew or should have known of
    the claim of the United States.

   In this case, KRAI argues that the district court erred in dis-
missing KRAI’s civil action on the ground that the action was
time barred, and in holding that such time bar deprived the
court of subject matter jurisdiction to hear KRAI’s action.

                                A

   [3] KRAI argues first that the QTA’s limitations period is
not a jurisdictional limitation on a court’s authority. We dis-
agree. The running of the twelve-year limitations period
deprives the federal courts of “jurisdiction to inquire into the
merits” of an action brought under the QTA. Block v. North
Dakota, 

, 292 (1983); Fidelity Exploration and
Prod. Co. v. United States, 

, 1186 (9th Cir.
2007). KRAI contends that Block’s jurisdictional ruling has
been superceded by subsequent decisions of the Supreme
Court holding that statutes of limitation and other require-
ments for bringing a claim under certain federal statutes (not
including the QTA) are not jurisdictional and therefore waiv-
able. See generally Arbaugh v. Y&H Corp., 

,
511-14 (2006) (holding that a statutory requirement in 42
U.S.C. §§ 2000e, 2000e-5(f) was an element of a cause of
action rather than a jurisdictional requirement); Scarborough
v. Principi, 

, 413-14, 420-21 (2004) (holding that
a pleading requirement in the Equal Access to Justice Act was
not jurisdictional and was therefore curable through subse-
quent amendment); Irwin v. Dep’t of Veterans Affairs, 

, 95-96 (1990) (holding that the time limits established
by 42 U.S.C. § 2000e-16(c) for suits by federal employees
against their government employers are not jurisdictional
12214           KINGMAN REEF v. UNITED STATES
because “the same rebuttable presumption of equitable tolling
applicable to suits against private defendants should also
apply to suits against the United States.”). KRAI’s reliance on
these cases is to no avail, because we are bound by our more
recent decision in Fidelity Exploration and Prod. Co. v.
United States, 

, 1186 (9th Cir. 2007), which
reaffirmed Block’s jurisdictional holding in the QTA context.
As we noted in Fidelity, in the absence of any Supreme Court
decision overruling Block, “we must follow the Supreme
Court precedent that directly controls, leaving to the Court the
prerogative of overruling its own prior 

(citing Rodriguez de Quijas v. Shearson/Am. Express,
Inc., 

, 484 (1989)).

   Moreover, the Supreme Court’s recent decisions have also
upheld “[j]urisdictional treatment of statutory time limits.”
Bowles v. Russell, 

, 2364-66 (2007). Bowles
held that the provisions of 28 U.S.C. § 2107 governing the
deadline for filing notices of appeal are “jurisdictional” and
cannot be tolled. 

John R. Sand & Gravel
Co. v. United States rejected the argument that Irwin permits
equitable tolling of all statutes of limitation on suits against
the government, and held that the Federal Court of Claims’
timeliness requirements were jurisdictional. 

,
753-56 (2008). Thus, Gravel Co. forecloses KRAI’s argument
that Irwin created a general rule superceding Block’s holding
as to the jurisdictional nature of the QTA’s twelve-year limi-
tations period. Nor can we accept KRAI’s argument that Irwin
and its progeny require us to reexamine Congress’s intent in
creating the twelve-year limitations period. The Supreme
Court has already held that Congress intended the QTA’s lim-
itations period to serve interests of finality, and therefore it
may not be tolled. See 

; United
States v. Beggerly, 

, 49 (1998).

  [4] KRAI next argues that the district court erred in dis-
missing the action on statute of limitations grounds under
Rule 12(b)(1) because the statute of limitations issue was
                KINGMAN REEF v. UNITED STATES              12215
intermeshed with the ownership issue. We disagree. In gen-
eral, a district court is permitted to resolve disputed factual
issues bearing upon subject matter jurisdiction in the context
of a Rule 12(b)(1) motion unless “the jurisdictional issue and
the substantive issues are so intermeshed that the question of
jurisdiction is dependent on decision of the merits.” Thornhill
Publ’g Co. v. Gen. Tel. & Elecs. Corp., 

, 735
(9th Cir. 1979); accord Augustine v. United States, 

, 1077 (9th Cir. 1983).

   [5] Here, the question whether this action was timely was
not inextricably intertwined with the ultimate merits issue of
ownership. As the district court correctly noted, “[t]he crucial
issue in the statute of limitations inquiry is whether the plain-
tiff had notice of the federal claim, not whether the claim
itself is valid.” Kingman 

(inter-
nal quotation marks omitted). Thus, the district court properly
addressed the jurisdictional issue of timeliness in the context
of Rule 12(b)(1).

   Finally, KRAI argues that the district court erred by requir-
ing KRAI to carry the burden of establishing that its claim
was timely. To support its argument that the United States
bore the burden to establish an absence of jurisdiction in this
case, KRAI cites to legislative history, in particular, a House
of Representatives committee report recounting the Justice
Department’s statement that “if the United States wished to
assert that the statute of limitation had run, it would then have
the burden of establishing this fact.” H.R. Rep. No. 92-1559
(1978), reprinted in 1972 U.S.C.C.A.N. 4547, 4551. Although
ordinarily the defendant bears the burden of proving an affir-
mative statute of limitations defense, here the statute of limi-
tations is jurisdictional, and, “[w]hen subject matter
jurisdiction is challenged under Federal Rule of Procedure
12(b)(1), the plaintiff has the burden of proving jurisdiction
in order to survive the motion.” Tosco Corp. v. Comtys. for
a Better Env’t, 

, 499 (9th Cir. 2001). However,
we need not determine who bears the burden of proving time-
12216           KINGMAN REEF v. UNITED STATES
liness for purposes of the QTA, because, as discussed below,
the evidence overwhelmingly establishes that more than
twelve years elapsed since the Fullard-Leos’ claim accrued.
See Intel Corp. v. Hartford Accident & Indem. Co., 

, 1558 (9th Cir. 1991).

                               B

   [6] An action brought under the QTA “accrues when the
landowner or his predecessors-in-interest knew or should
have known of the United States’ claim.” 

; see 28 U.S.C. § 2409a(g). The QTA’s “statute of limita-
tions applies retroactively,” so it is irrelevant whether KRAI’s
predecessors in interest, the Fullard-Leo family, was put on
notice of the United States’s interest before or after the enact-
ment of the QTA. Donnelly v. United States, 

,
1318 (9th Cir. 1988) (citing 

).

   [7] The record makes clear that the Fullard-Leos had actual
notice that the United States claimed an interest in Kingman
Reef more than twelve years prior to the filing of the com-
plaint in this case. As noted above, in their April 20, 1937 let-
ter, the Fullard-Leos acknowledged that Kingman Reef’s
“ownership presumably rests with the State or Navy depart-
ment.” Kingman 

. When the
Fullard-Leos subsequently threatened the Navy with legal
action to establish their ownership interest, the Navy
expressly rejected their claim by letter of April 26, 1938, con-
cluding that the evidence was “not sufficient to uphold the
claim of Mrs. Fullard-Leo” to Kingman Reef. 

These communications between the Fullard-Leos and the
Navy Department demonstrate conclusively that KRAI’s
“predecessor in interest knew or should have known of the
claim of the United States” by April 26, 1938, at the latest.
§ 2409a(g); see Michel v. United States, 

, 132 (9th
Cir. 1995).
                  KINGMAN REEF v. UNITED STATES                 12217
   [8] KRAI argues that the Fullard-Leos’ correspondence
with the United States Navy did not cause its claim to accrue
for purposes of § 2409a(g) because “[a]ny claim that the gov-
ernment derived ownership of Kingman from either the
Guano Act4 or the 1934 [Executive] Order would have made
no sense to any person.” KRAI’s attack upon the ultimate
validity of the United States’s claim does not overcome the
fact that its QTA claim “accrued on the date the plaintiff or
his predecessor in interest knew or should have known of the
claim of the United States.” § 2409a(g). It is irrelevant
whether the United States’s justifications for rebuffing the
Fullard-Leos’ claims of ownership and rejecting requests for
compensation were meritorious; the QTA limitations period
accrues as soon as the United States makes a “claim that
creates even a cloud on” a plaintiff’s ownership interest. See

; California ex rel. State Land Comm’n
v. Yuba Goldfields, Inc., 

, 396 (9th Cir. 1985);
see also Spirit Lake Tribe v. North Dakota, 

, 738
(8th Cir. 2001) (“The government’s claim need not be clear
and unambiguous. . . . All that is necessary is a reasonable
awareness that the Government claims some interest adverse
to the plaintiff’s.”) (internal quotation marks omitted).
Regardless of the merits of the United States’s claim to King-
man Reef, the Fullard-Leos’ acknowledgment that the United
States claimed ownership of the reef is sufficient for their
claim to accrue under the QTA.

   [9] Because KRAI’s claim accrued as of April 26, 1938, the
federal court would lack subject matter jurisdiction as of April
27, 1950, absent some exception to the statute of limitations
in § 2409a(g). See 

; 

.
  4
    The Guano Islands Act authorizes the President to “consider[ ] as
appertaining to the United States” any unclaimed island “[w]henever any
citizen of the United States discovers a deposit of guano” thereon. 48
U.S.C. § 1411.
12218           KINGMAN REEF v. UNITED STATES
                               C

   KRAI argues that even if its predecessors in interest should
have known that the United States had claimed an interest in
Kingman Reef at one time, the United States subsequently
abandoned that interest and the statute of limitations under the
QTA has not run on any new claim to Kingman Reef asserted
by the United States. In support of its argument that the
United States abandoned its interest in Kingman Reef during
the period between 1938 and December 11, 2000 (the date the
United States established the Kingman Reef National Wildlife
Refuge), KRAI relies on two types of evidence: evidence that
the United States did not restrict access to Kingman Reef, see

, and evidence that government
employees agreed that the Fullard-Leos owned the reef, see

-33.

   First, KRAI notes that Navy employees did not restrict the
public’s access to Kingman Reef. For example, Navy employ-
ees obtained the Fullard-Leos’ permission to access the reef,
instructed members of the public to contact the Fullard-Leos
for permission to enter, and indicated a belief that the regula-
tions restricting access to the reef area had been suspended.

   KRAI relies on Shultz for the proposition that these actions
constituted abandonment of the United States’s claim of inter-
est in Kingman Reef. In Shultz, we held that the plaintiffs’
claim under the QTA to quiet title to plaintiffs’ easement over
a road adjacent to a federal military base originally accrued
when Shultz had reasonable notice that the government
denied Shultz’s right of access to the road. If this denial had
occurred more than twelve years before Shultz brought his
claim, Shultz’s action would have been time barred unless,
after the claim accrued, “the government’s failure to restrict
access to the base . . . led Shultz or his predecessors-in-
interest reasonably to believe that the government did not
continue to claim an interest in the 

. In other words, if the United States stopped denying
                KINGMAN REEF v. UNITED STATES            12219
Shultz access to the use of the road, Shultz could have reason-
ably believed that the United States had abandoned its claim
to exclusive use of the road. In such a case of abandonment,
Shultz’s claim would accrue “when the government reasserted
a claim,” not when the government originally denied Shultz’s
access. 

the district court noted, however, Shultz does not
apply directly to this case, because KRAI is asserting an own-
ership interest over government property, which is different
from a plaintiff’s claim of an easement. See, e.g., McFarland
v. Norton, 

, 726-27 (9th Cir. 2005); Warren v.
United States, 

, 1337 (D.C. Cir. 2000) (citing

). Even if a reasonable plaintiff could
believe that the United States had abandoned its claim that the
plaintiff did not have an easement over government property
by allowing the plaintiff access to the property, see 

, a reasonable plaintiff could not believe that
the United States had abandoned its claim of a possessory
interest in public lands merely because it failed to enforce
restrictions upon public access. See 

. It is well established that the United States does not
abandon its claims to property by inaction. See United States
v. California, 

, 40 (1947). As the Supreme Court
explained:

    The Government, which holds its interests here as
    elsewhere in trust for all the people, is not to be
    deprived of those interests by the ordinary court
    rules designed particularly for private disputes over
    individually owned pieces of property; and officers
    who have no authority at all to dispose of Govern-
    ment property cannot by their conduct cause the
    Government to lose its valuable rights by their acqui-
    escence, laches, or failure to act.

the United States lose property rights through
adverse possession. See United States v. Pappas, 

          KINGMAN REEF v. UNITED STATES
1342, 1343 n.3 (9th Cir. 1987) (“One cannot gain title to land
of the United States through adverse possession.”); see also
§ 2409a(n) (precluding QTA “suits against the United States
based upon adverse possession”). In light of these settled prin-
ciples, the Fullard-Leos could not have reasonably construed
the United States’s failure to exclude the public from King-
man Reef as an abandonment of its claim of interest. See
Kingman 

n.10. We must there-
fore reject KRAI’s first argument that the failure of Navy
employees to restrict the public’s access to Kingman Reef
evidences an abandonment of the government’s claim.

   Second, KRAI notes actions by various government
employees that are consistent with KRAI’s claim of owner-
ship. For example, a number of Navy and Fish and Wildlife
Service employees either acknowledged the Fullard-Leos’
ownership explicitly or implied such ownership through
offers to purchase the reef. KRAI relies on Michel for the
argument that government employees’ acknowledgment that
the Fullard-Leos owned Kingman Reef constituted an aban-
donment of the United States’s claim. 

. In
Michel, we considered the Michels’ claimed access easement
through a national wildlife refuge and held that the Michels’
claim accrued when “the Michels knew or should have known
the government claimed the exclusive right to deny their his-
toric access to the trails and roads across the refuge.” 

Although the district court concluded that the Michels
knew of the governments’ denial of access more than twelve
years before the Michels brought their claim, we concluded
there was evidence that the government had abandoned and
then reasserted its claim. Specifically, we held a letter from
the government to the Michels acknowledging their “ ‘historic
right of access’ appears to abandon any previously asserted
claim of exclusive control of that right.” 

We also
held that an agreement between the Michels and the govern-
ment that allowed access by the Michels as agreed to in the
earlier letter “could be construed as an abandonment of the
                KINGMAN REEF v. UNITED STATES              12221
government’s claim that it had the exclusive right to control
access.” 

that the actions and communications by gov-
ernment employees evidencing their belief that the Fullard-
Leo family owned Kingman Reef are analogous to the letter
and agreement in Michel, and “could be construed as aban-
donment of the government’s claim” of a property interest in
Kingman Reef. We disagree. As we explained in Shultz, the
key inquiry is whether these actions and communications
would give KRAI or its predecessors in interest “reason to
believe the government did not continue to claim an interest”
in the 

. In Michel, the property
interest at stake was not the government’s ownership interest
in the property, but merely the right to deny the Michels’
claimed access easement. Moreover, the government had
issued the Michels both a letter and a signed agreement
expressly recognizing their “historic right of access.” 

. Under these circumstances, a reasonable per-
son could believe that the United States had abandoned its
denial of the plaintiffs’ easement right.

    [11] By contrast, where the United States’s claim of interest
in property stems from formal actions of the legislative or
executive branch, a person could not reasonably conclude that
informal remarks of agency personnel or internal agency
memoranda could eliminate the cloud upon the property’s
title. See Spirit Lake 

(holding that
an informal opinion memorandum by an Associate Solicitor
in the Department of Interior did not establish abandonment
because “intra-office memoranda do not bind the govern-
ment”). In a real estate transaction, a reasonable prospective
purchaser intending to buy property free of any clouds on the
title would require clear evidence that all adverse claims of
ownership had been relinquished, as documented by a person
with appropriate authority, and would not rely on informal let-
ters and memos from low-level employees.
12222               KINGMAN REEF v. UNITED STATES
   [12] Our conclusion that some more formal step by the
United States was necessary to give KRAI “reason to believe
the government did not continue to claim an interest” in the
property, 

, is consistent with the QTA
itself, which established a formal method for the United States
to disclaim any interest in property, specifically by filing such
a disclaimer with the court. See 28 U.S.C. § 2409a(e).5 As
§ 2409a(e) makes clear, Congress did not deem unofficial
statements by government officials to be sufficient to elimi-
nate the United States’s claim of interest in property and to
thus deprive the district court of jurisdiction under the QTA.
Therefore, we agree with the Eighth Circuit that the United
States cannot be deemed to have abandoned a claim of owner-
ship for purposes of § 2409a(g) unless it “clearly and
unequivocally abandons its interest,” Spirit Lake 

, as evidenced by documentation from a govern-
ment official with authority to make such decisions on behalf
of the United States.

   [13] Here, there is no evidence in the record that an appro-
priate government official clearly and unequivocally aban-
doned the United States’s interest in Kingman Reef. The
district court found that KRAI presented evidence only “of
confusion and mistake on the part of some government
employees,” as to whether the United States ultimately pos-
sessed an ownership interest in Kingman Reef, Kingman 

n.11, and this conclusion is not
clearly erroneous. The government has not rescinded the
  5
   Section 2409a(e) of the QTA provides:
      If the United States disclaims all interest in the real property or
      interest therein adverse to the plaintiff at any time prior to the
      actual commencement of the trial, which disclaimer is confirmed
      by order of the court, the jurisdiction of the district court shall
      cease unless it has jurisdiction of the civil action or suit on
      ground other than and independent of the authority conferred by
      section 1346(f) of this title.
28 U.S.C. § 2409a(e).
                  KINGMAN REEF v. UNITED STATES                   12223
Executive Orders designating Kingman Reef as public land
under Navy protection, nor has the regulation establishing the
Kingman Reef Naval Defensive Sea Area been repealed. See
32 C.F.R. § 761.3(a)(2)(v), (b)(2); Exec. Order Nos. 6935,
8682.6 Neither has any United States official with authority to
bind the Executive Branch clearly and unequivocally dis-
claimed the United States’s claim of interest in Kingman
Reef. Although at various times correspondence and internal
memoranda from employees and officials of various Execu-
tive Branch agencies reflect an understanding that the Fullard-
Leo family owned, or claimed ownership of, Kingman Reef,
none of the documents in the record indicate an official deter-
mination that the United States no longer claimed a property
interest in the reef or intended to disclaim such an interest.
Therefore, KRAI and its predecessors in interest could not
reasonably conclude that the recent informal governmental
communications had eliminated the cloud upon the title to
Kingman Reef created by official government actions in the
1930s. Accordingly, we reject KRAI’s theory that the United
States abandoned its claim.

                                   D

    [14] Finally, KRAI contends that the United States was
equitably estopped from raising the twelve-year limitations
period of § 2409a(g) as a defense to KRAI’s claim. KRAI
asserts that the United States concealed its intention to annex
Kingman Reef while negotiating with the Fullard-Leo family
to purchase Palmyra Atoll, so that it could ensure successful
purchase of Palmyra (over which it had no plausible claim of
title) without expending funds to obtain Kingman Reef. We
reject this argument. As we have noted, § 2409a(g) is jurisdic-
  6
   KRAI notes that the Naval Airspace Reservation over Kingman Reef
has been suspended. See 32 C.F.R. § 761.4(d)(1). However, the suspen-
sion of airspace restrictions did not repeal the Naval Defensive Sea Area
reservations in their entirety. See 

(b)(2); Kingman

.
12224           KINGMAN REEF v. UNITED STATES
tional under our precedents, e.g., 

,
and “subject-matter jurisdiction . . . can never be forfeited or
waived.” 

(internal quotation marks
omitted). KRAI notes Justice Stevens’s concurring opinion in
Beggerly, which states that the Court was “not confronted
with” and “need not . . . address” the question whether “equi-
table estoppel might apply if the Government were guilty of
outrageous misconduct that prevented the plaintiff, though
fully aware of the Government’s claim of title, from knowing
of her own 

(Stevens, J., concur-
ring). We need not address the effect, if any, of Justice Ste-
vens’s concurrence. As noted above, the district court found
no evidence of outrageous conduct, and thus did not abuse its
discretion in holding that KRAI failed to establish the ele-
ments of a claim of equitable estoppel. See Morgan v. Gon-
zales, 

, 1092 (9th Cir. 2007).

  AFFIRMED.