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

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.wn I~upatki erosion cycles, the Colorado qiver cut some 760 m
(2,500 feet) into the Mar~le and Grand canyons during this time.

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Holocene Alluvial Terraces in the Colorado River SysteM
Alon9 the Colorado and Little Col oradoRi vel" systems, Holocene
alluvial terraces generally consist of finer textured sediments than the
Pleistocene terraces. We may conclude then that Holocene discharges
have been generally of lesser magnitude than during the Pleistocene.
The classic subdivision of late Pleistocene/Holocene alluvial deposits
in northeastern Arizona by Hack (1942) includes the late Pleistocene
Jeddito Formation, the post-Altithermal Tsegi Formation, and the latest
Holocene Naha Formation.
T. Karl strom, Gunennan, and Eul er (1974) have further subdivided
the late Holocene alluvial sequence in northeastern Arizona. Based on
C14, tree-ring and archeological dating of point boundaries (soils and
diastems) which separate alluvial units in a whole series of alluvial
valleys in northea:;tern Arizona, T. Karl strom subdivides alluvium of the
last 2,UOO years into the following units: (1) "w" alluvium, deposited
during regionally moister periods which occurred between main drought
intervals dated at about 250 B.C. and A.D. 350; (2) "XII alluvium,
deposited between drought interval s which centered at about A. D. 350 and
875; (3) "y" alluvium, deposited between about A.D. 875 and 1450;
(4) "Z" alluvium, deposited he tween ahout A.D. 1450 and 1900, and
(5) "All alluvium, deposited since A.D. 1900.
Hereford's (l984a) IICottonwood terrace" along the Little Colorado
River correlates with the Naha Formation and tle "Zll terrace, and like
those, was dissected during the 1890 to 190(1 arroyo cutting epi sode
which occurred throughout the Southwest.

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Processes of Terrace Formation and
the Cl imatic Signi ficance of Terraces
Streams aggrade or de<]l~ade in response to a number of environmental
factors and/or al terati ons in the fl uvi al system i tsel f( Schumm 1977).
In the fluvial system, discharge, sediment load and base level are
considered to be independent variables; channel width, depth, bed
roughness, groin size of sediment load, velocity, and channel pattern

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