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<br />1-10 . Chapter 1
<br />
<br />Reaion 0 (Lees Ferry to Kwaaunt
<br />Rapid)
<br />This region was 90.1 km (56.0 mi) long from Lees
<br />Ferry to Kwagunt Rapid (RM 0.0-56.0) and was
<br />characterized by four geomorphic reaches--Permian
<br />Section, Supai Gorge, Redwall Gorge, and the upper
<br />portion of Lower Marble Canyon (Table 1-3).
<br />Average channel widths in the four reaches were 79
<br />64, 67, and 107 m (280, 210, 220, and 350 ft):
<br />respectively, and channel slope was low to moderate
<br />(Schmidt and Graf 1990). Substrate was composed
<br />of36-81% bedrock and boulders, and the shoreline
<br />was typically talus with intermittent tributary
<br />alluvial fans, sand bars, or earthen banks with
<br />vegetation.
<br />
<br />Shoreline features in Region 0 (Fig. 1-5) are fonned
<br />primarily by the Toroweap Fonnation and Coconino
<br />Sandstone (RM 2.0-5.0); Hermit Shale (RM 5.0-
<br />11.3); the Supai Group, including Esplanade
<br />Sandstone (RM 11.3-15.0); Wescogame,
<br />Manakacha, Watahomigi, and Surprise Canyon
<br />Formations (RM 15.0-23.0); Red Wall Limestone
<br />(RM 22.6-35.9); and Muav Limestone (RM 37.0-
<br />56.0).
<br />
<br />The Patia River (RM 1.0) and Nankoweap Creek
<br />(RM 52.2) are the only perennial tributaries in this
<br />region. Several local drainages flow intermittently
<br />during rain spates in June, July, and August,
<br />introducing large amounts of sediment into the river.
<br />The largest contributor of sediment to this upper
<br />portion of the study area is the Paria River. Large
<br />alluvial fans at tributary inflows in this region
<br />constrict the channel and form 12 minor and 6 major
<br />rapids (Badger Creek, Soap Creek, House Rock,
<br />North Canyon, 2 I-Mile, Nankoweap).
<br />
<br />Reaion I (Kwaaunt Rapid to Hance
<br />Rapid)
<br />Region I was 34.4 kIn (21.4 mi) long from Kwagunt
<br />Rapid to Hance Rapid (RM 56.0-77.4) and was
<br />characterized by two geomorphic reaches--Lower
<br />Marble Canyon and Furnace Flats (Table 1-3). The
<br />river channel in these reaches averaged 107 and 119
<br />m (350 and 390 ft) in width, respectively, and
<br />channel slope was low to moderate at 0.10 and 0.21
<br />%, respectively. Substrate was composed of 30-36
<br />% bedrock and boulders, and shoreline was typically
<br />talus, ledges, or vertical cliffs with intermittent
<br />
<br />Final Report
<br />
<br />tributary alluvial fans, sand bars, or earthen banks
<br />with vegetation.
<br />
<br />Shoreline features in Region I are fonned primarily
<br />by Bright Angel Shale (RM 47.0-58.0), Tapeats
<br />Sandstone (RM 58.0-63.0), and the Unkar Group
<br />(RM 63.0-77.4) of the Great Unconformity. Soft
<br />shales and sandstones of Bright Angel Shale and
<br />Tapeats Sandstone create characteristic ledges and
<br />shorelines with fractured and collapsed rock
<br />fragments.
<br />
<br />The Precambrian sedimentary series first appears in
<br />the Nankoweap Formation as an angular
<br />unconformity at RM 63.0 and, from that point to
<br />RM 65.5, the shoreline is characterized by steep
<br />vertical walls and talus with large angular blocks.
<br />Cardenas Basalt and Dox Sandstone of the Unkar
<br />Group are angularly juxtaposed downstream of the
<br />Palisades Fault so that from Lava Canyon (RM
<br />65.5) to Escalante Creek (RM 75.0), the channel is
<br />wider and the shoreline is composed of boulders and
<br />cobble, with intermittent talus and occasional
<br />vertical walls.
<br />
<br />The only perennial tributary in Region I is the LCR
<br />(RM 61.3), which is the largest tributary in Grand
<br />Canyon and the largest contributor of sediment to
<br />the Colorado River in Grand Canyon. Large alluvial
<br />fans form 9 minor and 6 major rapids (K wagunt,
<br />60-Mile, Lava Canyon, Tanner, Unkar, Nevills) in
<br />this region.
<br />
<br />Reaion II (Hance Rapid to below
<br />Havasu Creek)
<br />Region II was 132.7 km (82.5 mi) long, and
<br />extended from Hance Rapid to below Havasu Creek
<br />(RM 77.4-159.9). This region was composed of
<br />four geomorphic reaches, including Upper Granite
<br />Gorge, Aisles, Middle Granite Gorge, and Muav
<br />Gorge (Table 1-3). Upper Granite Gorge (RM
<br />77.4-117.8) had the lowest average ratio of top
<br />canyon width to mean depth (7), the second
<br />narrowest average channel width (60 m, 190 ft), and
<br />the steepest channel slope (0.23%) of any
<br />geomorphic reach in Grand Canyon. The river in
<br />Upper Granite Gorge flows primarily through
<br />Vishnu Schist (black), Zoroaster Granite (pink), and
<br />Hotauta Conglomerate. These are resistant
<br />Precambrian formations about 1.8 billion years old
<br />
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