FOR PUBLICATION
 UNITED STATES COURT OF APPEALS
      FOR THE NINTH CIRCUIT

UNITED STATES OF AMERICA,                  No. 06-30614
                Plaintiff-Appellee,
               v.                            D.C. No.
                                          CR-05-00061-RFC
EUGENE RAYMOND RISING SUN,
                                             OPINION
             Defendant-Appellant.
                                      
       Appeal from the United States District Court
               for the District of Montana
       Richard F. Cebull, District Judge, Presiding

                 Argued and Submitted
         September 26, 2007—Seattle, Washington

                   Filed April 14, 2008

    Before: Betty B. Fletcher, Andrew J. Kleinfeld, and
            Ronald M. Gould, Circuit Judges.

                 Opinion by Judge Gould




                           3867
                 UNITED STATES v. RISING SUN            3869


                        COUNSEL

Mark S. Werner, at argument, & Anthony R. Gallagher, on
the briefs, Federal Defenders of Montana, Billings, Montana,
for appellant Eugene Rising Sun.

Corey Endo, at argument, and William W. Mercer & Lori
Harper Suek, on the briefs, U.S. Attorney’s Office, Billings,
Montana, for appellee United States.
3870             UNITED STATES v. RISING SUN
                         OPINION

GOULD, Circuit Judge:

   Eugene Rising Sun (“Rising Sun”) appeals two consecutive
life sentences which were imposed after he pled guilty to two
counts of second-degree murder. He argues that the sentenc-
ing court erred in applying the enhancement found at
U.S.S.G. § 3A1.1(b)(1) for vulnerable victims because of the
remote location where the murders occurred and in applying
the enhancement found at U.S.S.G. § 3C1.1 for obstruction of
justice because he threatened a witness and tried to destroy
evidence before the police investigation began. Rising Sun
also argues that the sentence was unreasonable. We have
jurisdiction to hear the appeal under 28 U.S.C. § 1291, and we
vacate and remand for resentencing.

                              I

   Koren Diebert was reported missing on November 22,
2003. Five days later her body, along with that of LaFonda
Big Leggins, was found in a ditch off Big Horn County Road
50A in Montana, which is part of the Crow reservation. An
autopsy revealed that both young women had died from blunt
force trauma to their heads caused by a heavy object.

   Investigations by law enforcement authorities determined
that Diebert and Big Leggins were last seen in the late eve-
ning of November 18 in the company of Rising Sun and his
two brothers. One witness told investigators that Rising Sun
had commented to her that “he had gotten rid of some of his
stuff because it was evidence.” Another witness reported see-
ing, on the morning of November 19, a maroon Corsica
parked at an abandoned house on the Crow reservation where
the Rising Sun family used to live. A third witness had linked
that same car to the murders of Diebert and Big Leggins. The
FBI obtained a search warrant for the abandoned house,
which was executed on December 5, 2003. In a trash can out-
                 UNITED STATES v. RISING SUN              3871
side the house, agents found items of clothing and jewelry
that appeared to have blood stains on them and that also
appeared to have been burned. DNA tests conducted on the
items seized from the trash can revealed that these items con-
tained blood from Diebert and Big Leggins.

   Rising Sun’s younger brother Moses was interviewed twice
by law enforcement personnel. During the first interview,
three days after Diebert was reported missing, he denied hav-
ing seen either of the young women after the early evening of
November 18. When interviewed again in January of 2004,
however, Moses admitted that on November 18, after a night
of heavy drinking, he and his two brothers had driven with
Diebert and Big Leggins to a remote area several miles south
of Harden, Montana so they could “party together.” Moses
said that the group decided to stop the car so that some of the
occupants could relieve themselves, and that when the vehicle
stopped, both Rising Sun and Big Leggins got out of it. Soon
thereafter, Moses heard “a thump” and a woman screaming.
He then saw Rising Sun “smack” Big Leggins and accuse her
of being a “narc.” According to Moses, Rising Sun dragged
Big Leggins into a nearby ditch and then chased after Diebert
and repeatedly hit her with an object he had obtained from the
trunk.

   Moses further stated that when the brothers returned to
their mother’s home later that night, Rising Sun took a shower
and placed the clothes he had been wearing in a plastic bag.
Moses also said that Rising Sun then told him not to tell his
girlfriend about what had happened, and that when Moses
said that he was going to tell, Rising Sun threatened him with
a knife.

   Rising Sun was indicted on one count of first-degree mur-
der on May 20, 2005. Pursuant to a plea agreement, he later
pled guilty to a superseding information charging him with
two counts of second-degree murder under 18 U.S.C.
§§ 1153(a) and 1111. As part of this plea agreement, Rising
3872                 UNITED STATES v. RISING SUN
Sun stated his willingness to serve consecutive sentences on
the two counts.

   After assigning a base offense level of 33 for each count
pursuant to the 2003 edition of the federal Sentencing Guide-
lines,1 the presentence report recommended applying two two-
level enhancements, one for vulnerable victims under
U.S.S.G. § 3A1.1(b)(1) because the killings occurred in a
remote location, and one for obstruction of justice under
U.S.S.G. § 3C1.1 because Rising Sun had attempted to
destroy evidence and had threatened his brother Moses to pre-
vent him from talking to his girlfriend about the murders. At
Rising Sun’s sentencing hearing in November 2006, the dis-
trict court adopted both of these enhancements over Rising
Sun’s objections and also imposed a three-level upward
departure based on Extreme Conduct and Criminal Purpose,
resulting in an adjusted offense level of 39. The applicable
sentencing range, taking into account Rising Sun’s criminal
history category of IV, was 360 months to life for each count
of second-degree murder. The district court then determined
that because of the heinous nature of these murders and Ris-
ing Sun’s violent criminal history, it would impose the maxi-
mum allowable sentence of life for each offense, with the
sentences to be served consecutively. This appeal followed.

                                    II

  We review a district court’s interpretations of the federal
Sentencing Guidelines de novo, its factual determinations for
  1
   Although a sentencing court ordinarily will apply the version of the
Guidelines in effect on the date of sentencing, if doing so would violate
the Ex Post Facto Clause of the United States Constitution, “the court shall
use the [version] in effect on the date that the offense of conviction was
committed.” U.S.S.G. § 1B1.11 (2006). The district court determined that
the Ex Post Facto Clause was implicated in Rising Sun’s case because the
base offense level for second-degree murder rose from 33 to 39 between
the 2003 and 2004 editions of the Manual. Accordingly, it was correct for
the district court to use the 2003 edition of the Guidelines Manual.
                  UNITED STATES v. RISING SUN               3873
clear error, and its application of the Sentencing Guidelines to
the facts as it has found them for abuse of discretion. United
States v. Kimbrew, 

, 1151 (9th Cir. 2005). If we
apply this framework to one of the issues presented in this
case, we review the district court’s determination that Diebert
and Big Leggins were vulnerable because they were assaulted
in a remote location as a factual finding for clear error, while
we review the conclusion that a two-level enhancement for
vulnerable victims was appropriate because of that remote set-
ting for abuse of discretion. See United States v. Weischedel,

, 1252, 1255 (9th Cir. 2000). If upon review
this court finds that the district court committed a “significant
procedural error,” see Gall v. United States, 

,
597 (2007), such as a “material error in the Guidelines calcu-
lation that serves as the starting point for the district court’s
sentencing decision, we will remand for resentencing pursuant
to 18 U.S.C. § 3742(f).” United States v. Cantrell, 

, 1280 (9th Cir. 2006). If no such material error in apply-
ing the Guidelines is found, however, we may go on to evalu-
ate the sentence for its substantive reasonableness under an
abuse of discretion standard. See 

; Can-

.

                              III

   Rising Sun argues that the “vulnerable victim” enhance-
ment described in U.S.S.G. § 3A1.1(b)(1) should not have
been applied to his sentence for two reasons. First, he con-
tends that no personal traits of either Diebert or Big Leggins
rendered them particularly susceptible to his criminal conduct.
Second, he suggests that the two victims voluntarily accompa-
nied him and his brothers to the remote location where they
were killed and were not lured there as part of a deliberate
scheme. We agree with the first of these objections and con-
clude that the “vulnerable victim” enhancement should not
have been applied in Rising Sun’s case because none of the
victims’ characteristics, alone or in combination with sur-
rounding circumstances of the crime, made them more vulner-
3874              UNITED STATES v. RISING SUN
able to Rising Sun’s criminal conduct than any other members
of the public.

   [1] Section 3A1.1(b)(1) of the U.S. Sentencing Guidelines
provides for a two-level enhancement where “the defendant
knew or should have known that a victim of the offense was
a vulnerable victim.” Application note 2 in the commentary
to this Guideline states that “ ‘vulnerable victim’ means a per-
son . . . who is unusually vulnerable due to age, physical or
mental condition, or who is otherwise particularly susceptible
to the criminal conduct.” § 3A1.1 cmt. n.2. We have inter-
preted the “otherwise particularly susceptible” language as
requiring the sentencing court to consider both the victim’s
characteristics and the “circumstances surrounding the crimi-
nal act.” United States v. Peters, 

, 1417 (9th
Cir. 1992). However, although circumstances are to be con-
sidered, we also have held that where none of the victims’
personal characteristics made them particularly susceptible to
the crime at issue, the enhancement should not have been
applied because nothing about the victims “render[ed] the
defendant’s conduct more criminally depraved” than if the
same crime had been perpetrated against others. See United
States v. Castellanos, 

, 111 (9th Cir. 1996).

   [2] We reconciled these two precedents in United States v.
Weischedel, explaining that in both Peters and Castellanos,
“we examined the personal traits of the victims and the spe-
cific circumstances in which the victims found themselves
when the crimes were committed, and asked whether there
were any characteristics or circumstances that made the vic-
tims particularly susceptible to the crime.” 

,
1254-55 (9th Cir. 2000). Weischedel involved a married cou-
ple who sought to steal a car by representing to a car salesman
that they were potential customers and asking him to accom-
pany them on a test drive. 

After the three had
driven to a remote area, the husband fatally shot the car sales-
man and the couple took possession of the vehicle. 

court at sentencing imposed the two-level “vulnerable
                  UNITED STATES v. RISING SUN                 3875
victim” enhancement on the ground that the salesman’s age
(sixty) and occupation, as well as the circumstances in which
he found himself in that he was driven to a remote location
by people he thought were customers, rendered him particu-
larly susceptible to the defendants’ criminal conduct. 

In affirming the district court’s application of the
enhancement, we held:

    Here the district court properly looked to the particu-
    larly vulnerable circumstances in which [the victim]
    found himself after being placed in the front seat
    with his killer behind him and driven to a remote
    spot, at the behest of persons he believed his job
    obligated him to accommodate. The district court did
    not abuse its discretion in imposing the “vulnerable
    victim” adjustment.

   The district court in this case, unlike the district court in
Weischedel, did not mention any characteristics of Diebert or
Big Leggins that made them particularly vulnerable victims.
Instead, the sentencing court focused exclusively on the
remote location in which the murders took place. The district
court reasoned that because of the uninhabited area in which
they found themselves, “the victims knew that there was no
avenue of escape” and “no possibility that anyone could assist
or stop” Rising Sun’s attack. Citing Weischedel, the sentenc-
ing court then concluded that the remote location of the mur-
ders was “one of those circumstances rendering the victim
otherwise particularly susceptible” under which the enhance-
ment could be applied.

  [3] In our view, a correct reading of Weischedel does not
support the district court’s conclusion. Specifically, it was a
crucial factual component of Weischedel that the car sales-
man’s job required him to go to a remote area designated by
someone he thought was a potential customer. Nothing in that
3876              UNITED STATES v. RISING SUN
case implied that the remote location where the victim was
shot would have been independently sufficient to support the
enhancement. Rather, we made clear that the circumstances
that made the victim particularly susceptible to the criminal
conduct resulted from the requirements of his job. See

. By contrast, in this case Die-
bert and Big Leggins were not obligated to accompany Rising
Sun, and there were no personal characteristics of either vic-
tim referred to by the district court that made them any more
likely than the average person to go with Rising Sun and his
brothers to the remote area where they were killed. If we were
to disregard this distinction and uphold a “vulnerable victim”
enhancement simply because the crime occurred in a remote
location, without reference to any characteristics particular to
the victim, we would be broadening the enhancement to the
point where it might be applied to almost any case where a
crime was committed in an unprotected or sparsely populated
area.

   [4] We do not hold that a remote location may never be
considered among the circumstances of the crime that may
bear on the applicability of the vulnerable victim enhance-
ment. Such an approach would not be appropriate given the
required case-by-case nature of this inquiry and the deference
we accord to district courts in their role as finders of fact. We
simply hold that there must be something about the victim
that renders him or her more susceptible than other members
of the public to the criminal conduct at issue. A remote crime
location alone is not enough to sustain this enhancement.
Accordingly, we hold that the district court in this case abused
its discretion when it applied the “vulnerable victim”
enhancement to Rising Sun’s sentence solely based on the
remote location in which Big Leggins and Diebert found
themselves when attacked. Because we find error in the appli-
cation of the “vulnerable victim” enhancement on this basis,
we do not reach Rising Sun’s alternative argument that the
enhancement can apply only if the victim is lured to the
remote location for a criminal purpose.
                  UNITED STATES v. RISING SUN                3877
                               IV

   We next address the issue of whether the district court
properly imposed the two-level enhancement found at
U.S.S.G. § 3C1.1 for obstruction of justice when Rising Sun’s
obstructive acts, threatening his brother not to talk about what
he had witnessed and attempting to destroy his blood-stained
clothing by burning it, both occurred before any police inves-
tigation had begun. Relying on circuit precedent, the language
of the Guideline, and its commentary, we conclude that this
enhancement should not have been applied.

    The 2003 version of the Sentencing Guidelines, under
which Rising Sun was sentenced, stated that “[i]f a defendant
willfully obstructed or impeded, or attempted to obstruct or
impede, the administration of justice during the investigation,
prosecution, or sentencing of the instant offense,” his offense
level should be increased by two levels. U.S.S.G. § 3C1.1.
We have previously held that this wording precluded the
imposition of the enhancement where the defendant’s obstruc-
tive conduct, secreting boxes of records in Costa Rica,
occurred at least eleven months before the commencement of
a criminal investigation against him for tax fraud to which
those records proved relevant. United States v. Ford, 

, 352 (9th Cir. 1993) (interpreting an earlier but identically
worded version of U.S.S.G. § 3C1.1). While the length of the
delay between the obstructive actions and the onset of an
investigation might offer a way of distinguishing Ford, a
more recent Ninth Circuit case has reaffirmed the strictness of
§ 3C1.1’s temporal requirement. In United States v.
DeGeorge, we held that a defendant’s perjury during his civil
trial, which took place before his criminal investigation for
mail fraud began, could not be considered an “obstruction
offense” because the text of § 3C1.1 requires that “the perjury
. . . occur ‘during the course of the [criminal] investigation.’ ”

, 1222 (9th Cir. 2004) (alterations in original).

   Application note 1 in the commentary to the 2003 version
of § 3C1.1 also supports the conclusion that the enhancement
3878              UNITED STATES v. RISING SUN
could only apply if an investigation or prosecution was
already in progress when the obstructive actions were taken.
That note stated that “[the obstruction] adjustment applies if
the defendant’s obstructive conduct . . . occurred during the
course of the investigation, prosecution, or sentencing of the
defendant’s instant offense of conviction.” U.S.S.G. § 3C1.1
cmt. n.1 (2003). The note was added by amendment in 1998
in order to clarify “the temporal element of the obstruction
guideline (i.e., that the obstructive conduct must occur during
the investigation, prosecution, or sentencing of the defen-
dant’s offense of conviction).” U.S.S.G. supp. to app. C,
Amend. 581 (1998). This application note removed any
ambiguity about the Sentencing Commission’s intent to
include a temporal restriction in § 3C1.1.

   [5] In applying § 3C1.1 to increase Rising Sun’s sentence,
the district court relied in part on subsection (d) of application
note 4 interpreting § 3C1.1, which lists examples of conduct
to which the obstruction enhancement would apply. These
examples include “destroying or concealing or directing or
procuring another person to destroy or conceal evidence that
is material to an official investigation or judicial proceeding
(e.g., shredding a document or destroying ledgers upon learn-
ing that an official investigation has commenced or is about
to commence).” § 3C1.1 cmt. n.4(d) (emphasis added). Appli-
cation notes like this one are treated as authoritative interpre-
tations of the Sentencing Guidelines, unless they violate the
Constitution or a federal statute or are inconsistent with, or a
plainly erroneous reading of, the Guideline they are meant to
interpret. See United States v. Powell, 

, 613 (9th
Cir. 1993) (citation omitted). When commentary and the
Guideline it interprets are inconsistent so that “following one
will violate the dictates of the other, the Sentencing Reform
Act itself commands compliance with the guideline.” Stinson
v. United States, 

, 43 (1993). Application note
4(d) is clearly inconsistent with the language of the Guideline
which requires that the obstructive conduct occur “during the
investigation, prosecution, or sentencing of the instant
                  UNITED STATES v. RISING SUN                   3879
offense.” U.S.S.G. § 3C1.1 (emphasis added). We therefore
apply our precedent holding that U.S.S.G. § 3C1.1 contained
a temporal restriction and that the enhancement could not
apply if the obstructive conduct occurred before the investiga-
tion began. See 

; 

.

   While most circuits that have addressed the issue of pre-
investigation obstruction and § 3C1.1, particularly in the wake
of the 1998 amendment, have followed our approach, many
have done so with reluctance. For example, the Sixth Circuit
in United States v. Baggett recognized that “[f]ollowing the
[1998] amendment, this circuit has adhered to . . . [a] strictly
temporal analysis” of § 3C1.1, but opined that “it seems
counter-intuitive to say that threats made by a defendant to
prevent a victim from reporting conduct that later results in a
conviction do not constitute obstruction of justice.” 

, 541-42 (6th Cir. 2003). Perhaps in response to such pol-
icy concerns, in 2006 the Sentencing Commission amended
this Guideline to remove the temporal dimension from
§ 3C1.1. The version in effect beginning with the 2006 edition
of the Guidelines provides:

    If . . . the defendant willfully obstructed or impeded,
    or attempted to obstruct or impede, the administra-
    tion of justice with respect to the investigation, pros-
    ecution, or sentencing of the instant offense of
    conviction, . . . increase the offense level by 2 levels.

§ 3C1.1 (2006) (emphasis added). Furthermore, the new
application note 1 in the commentary to § 3C1.1 states that
“[o]bstructive conduct that occurred prior to the start of the
investigation of the instant offense of conviction may be cov-
ered by this guideline if the conduct was purposefully calcu-
lated, and likely, to thwart the investigation or prosecution of
the offense of conviction.” 

cmt. n.1. This applica-
tion note would appear to be an almost letter-perfect descrip-
tion of the conduct that Rising Sun engaged in after
3880              UNITED STATES v. RISING SUN
committing the murders; nonetheless, it cannot be applied to
his case.

   [6] Although Rising Sun was sentenced in November of
2006, his sentence was calculated based on the 2003 edition
of the Guidelines in order to avoid an Ex Post Facto Clause
violation. See U.S.S.G. § 1B1.11(b)(1). Where an earlier edi-
tion of the Guidelines is used, that earlier edition must be used
in its entirety with one exception: “the court shall consider
subsequent amendments, to the extent that such amendments
are clarifying rather than substantive changes.” 

Amendment 693 to the Guidelines in 2006,
which changed the language of § 3C1.1 to omit the temporal
requirement and added new application note 1 on pre-
investigation conduct, was not described as a clarifying
amendment. Rather, its stated purpose was to resolve “a cir-
cuit conflict regarding the issue of whether pre-investigative
conduct can form the basis of an adjustment under § 3C1.1.”
U.S.S.G. supp. to app. C, Amend 693 (2006). This was a sub-
stantive change, not merely a clarification, and so this amend-
ment cannot properly be considered in determining Rising
Sun’s sentence. Consequently, the district court abused its dis-
cretion in applying the two-level “obstruction of justice”
enhancement solely on the basis of actions that Rising Sun
took before an investigation had begun.

                               V

   Because we conclude that material errors affected the
Guidelines calculation that served as the starting point for the
district court’s sentencing decision, we vacate Rising Sun’s
sentence and remand this matter for resentencing. See 

(2007) (holding that “the appellate court
must . . . first ensure that the district court committed no sig-
nificant procedural error” and should consider the substantive
reasonableness of the sentence only if “the district court’s
sentencing decision is procedurally sound”); United States v.
Carty, No. 05-10200, 

, at *5 (9th Cir. March
                  UNITED STATES v. RISING SUN                3881
24, 2008) (en banc) (“On appeal, we first consider whether
the district court committed significant procedural error . . .”);
United States v. Can

(“[A] material
error by the district court in calculating the applicable Guide-
lines range is grounds for resentencing, just as it was before
Booker.”). We therefore decline to reach Rising Sun’s argu-
ment regarding the reasonableness of his sentence under
Booker.

  VACATED AND REMANDED.