9510

• UCREFRP Catalog Number: 9510
• Author: Jones, A. T.
• Title: A Cross Section of Grand Canyon Archeology
• USFW Year: 1986.
• USFW - Doc Type: Excavations at Five Sites Along the Colorado River.
• Copyright Material: NO

suggests that the spruce-fir zone extended to below 1,500 m
(4,921 feet). Juniper woodl and vegetati on is thought to have descended
to the 1 eve 1 of the Colorado Ri ver duri ng thi s ti me.
Osci1l atory warmi ng probably occurred since about 15,000 years
Before Present (B.P.). The Holocene, or present interglacial, is
arbitrarily placed at 10,000 years B.P. Climate has continued to
fluctuate during this period, but changes have been of lower magnitude.
Although sensitive paleoclimatic indicators record many high frequency
climate oscillations rluring this time (Euler and others 1979), Antevs'
(1955) three-fold subdivision of the Holocene is stil,l a useful
generalization. This model includes a relatively cool, moist Anathermal
between about 10,000 and 8,000 years B.P., a warmer and drier
Altithermal between ahout 8,000 and 5,000 'years B.P.., and a
progressively cool ing r'1edithermal from 5,000 years ago to the present.

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The Colorado River in the Grand Canyon Today

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The Colorado Ri ver ranges fror.1 about 23 to over 91 m (76 to over
300 feet) wide and about 11 to 26 m (35 to 85 feet) deep (Leopold 1969).
Actual depth to hedrockhas not been established throughout the course
of the river ahdprobably varies considerably. The river drops an
average of 4 rn/krn (8 feet/mil e) through the canyon, and most of thi s
drop occurs in about 160 rapids that make up only 9 percent of the
distance of the river. The rapids are spaced an average of 2.6 km
(1.6 miles) apart and are generally fomed by: (1) fans of rock debris
washed in from tri butary canyons, (2) outcrops of resi stant rock, or
(3) gravel bars in the channel. Pools, spaced fairly evenly between the
rapids, reach the greatest depths and are floored mostly by sand, silt
and clay size particles.
Prior to construction of the Glen Canyon dam in 1964, fluctuations
in discharge varied with seasonal precipitation and snow-melt
fluctuations. Recorded pre-dam discharge values ranged from a low of
about 81 m3 (2,870 cubic feet per second Lcfs]) in 1956 to a high of
about 5,663 m3 (200,000 cfs) in 1921, with an estimated high flO\-i of
about 8,495 m3 (300,000 cfs) occurring in 1882 (Stevens 1983). Sediment
loads carried by the river measured over a 50 year period prior to the

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