WSP05862

• File Number: 8220.101.10
• Description: Colorado River-Water Projects-Glen Canyon Dam/Lake Powel-Glen Canyon Adaptive Management
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 1/1/2005
• Author: DOI-USGS
• Title: Sedimentology and Stratigraphy of the Palisades Lower Comanche and Arroyo Grande Areas of the Colorado River Corridor Grand Canyon Arizona
• Water Supply Pro - Doc Type: Report/Study

14

Sedimentology and Stratigraphy of the Palisades, Lower Comanche, and Arroyo ,~~~ flIeas of the Colorado River

by dune migration and playa accumulation; a small !lumber
of local precipitation or high-wind events could have resulted
in episodically rapid accumulation of sediment in some loca-
tions. If. alLematively. unit 8 of section 4 is interpreted to be a
deposit resulting from the higher-stage 1884 flood inSlead of
the 1921 flood. this implies that unit F must be related to a pre-
historic flood event and thai erosion has removed the record of
the 1921 flood at the location of this profile.

Palisades Site Summary

Stratigraphic sections documented at Palisades indicate
repeated inundation of this area by Colorado River floods
in predam lime. Fluvial deposits containing climbing ripple
structures were present in three of the four vertical sections
studied in detail. and the fourth (section 3) contained sediment
for which fluvial deposition was suspected but could not be
confinned by sedimentary stmctures. The presence of spatially
extensive fluvial deposits indicates that virtually al] of the area
between canyon walls in the Palisades region was submerged
episodically during predam high flows; the upstream (north-
ward) migration direction offluviClI ripples indicates that an
eddy existed on river leti in this area (compare the slackwater
deposits of Kochcl and Baker. 1982, and channel-widening
deposits of Benilo and others. 2003). The upstream-tilted
water-surface slope apparent in dritiwood lines from both
the 1884 and 1921 floods provides additional evidence for a
large eddy existing on river left in this area at dis<.:harges at
or above 4,X 1 0 m'/s (170.000 ft'/s). Ii is possible that fluvial
deposits that underlie modem playa deposits on the east em
edge of the Palisades study area may have fonned in relation
to ponding of water upstream of ancient debris flows. Several
active debris fans exist close to and downstream of this area,
including Espejo (river mile 67.4), Comanche (mile 67.7). and
Tanner (mile 69.0) Creeks. Altemalively. these fluvial deposits
may have been emplaced in an eddy return channel during
flood recession. Figure 12 illustrates the decreasing influence
ot~fluvial deposition with distance from the river.
Reworking offluvia! sediment by wind-in this arca
appears to be common. In several of the stratigraphic sec-
tions, aeolian deposits were observed between or in close
association \\:ith fluvial deposits (compare Benito and others.
2003): aeolian material also was found commonly interbed-
ded with locally derived playa sediment in sections 3. and 4.
Playa sediment fonned a volumetrically minor component of
these stratigraphic sections. but the number of playa horizons
indicates that such deposits frequently intemlpt the record
of aeolian deposition. The present-day surface geomorphol-
ogy includes aeolian dunes that have been covered tu varying
degrees by vegetation and cryptogamic Cnlst. Burial of drift-
wood logs associated with the 1884 and 192 1 Colorado River
t100ds by aeolian dunes indicates active dune migration as
recently as Ihe early 20,h century. Presenl morphology of most
dunes in tht: Palisades area is consistent with relative inactiv-
ity; cryptogamic cmst fonnation, colonization by grasses, and

deflation features suggest that most dunes are relatively inac-
tive. One exception is a dune -2 m high that is migrating in a
northward direction and filling in a shallow branch of the main
arroyo net\vork at the location of archaeological site C: 13: 100
(appendix I; fig. 38).
The influence of locally derived sediment increases land-
ward and toward the debris fan (fig. 12). Slope-wash andlor
playa sediments are readily apparent in sections 2, 3, and 4.
Driftwood logs associated with Ihe 1884 and 1921 floods are
also partly buried by debris-fan and colluvial sediments in the
do\\.'nstream part of the study area. Three of the nine Palisades
archaeological sites (C: 13;98, C: 13;272, and C: 13:355) are
located within the range of influence of the Palisades Creek
debris fan, while a fourth (C: 13:33) is built 011 sediment
derived from a second debris fan. Of the nine sites, six were
apparently constmcted in or on fluvial sediment at least in
part, with or without aeolian reworking (C: 13:99. C: 13: 100,
C: 13:272. C: 13:334, C: 13:336, and C: 13:355). Four of the
nine archaeological sites (C:13:99, C:13:100. C:13:272. and
C: 13:336) have been preserved at least in part by a cover
of aeolian sediment. with minor contributions from aeolian
sedimentary cover at two additional sites (C: 13: 101 and
C: 13:335). Erosion associated with arroyo cutting is affect-
ing two of the sites (the large C: 13:99 site in the arca of Ihe
main arroyo net\vork, and C: 13:355). Exposure of the site can
be attributed at least in part to aeolian deflation at five of the
siles IC:13:99, C:13:100. C:13:IOI, C:13:272. and C:13:336).
Gellis (1994) reported that camping activity may have accel-
erated erosion in the Palisades area; because of relocation of
trails and other mitigation measures implemented by the NPS
since 1994, this is not believed to be a major impact agent at
these archaeological sites currently (National Park Service,
2004).

Lower Comanche Area

Geomorphic Setting

TIle Lower Comanche study area is shown in figure 13,
with a detailed view of the arroyo in which the majority of the
stratigraphic sections were located shown in figure 14. Like
Palisades, Lower Comanche falls within the Furnace Flats
geomorphic reach defined by Schmidl and Graf (1987). The
region studied for this project lies downstream of the Coman.
che area discussed by Thompson and Potochnik (2000) in their
survey of drainage catchment areas and alluvial terrace inci-
sion.
The canyon in this area remains wide. and Precambrian
Dox Fonllation is exposed at the river's edge on river right.
On river left in the vicinity of the study area, Pleistocene
debris-flow deposits tens of meters thick are present (Machette
and Rosholt, 1989; Pederson and others. 2004). Riverward
of the relict debris fans, large (> 10m high) sand dunes fonn
a large dune field (fig. 13). Many of Ihe dunes in this field
show evidence of active aeolian transport, though grasses