Skip to main content
U.S. flag

An official website of the United States government

Geologic map of the Blythe 7.5' quadrangle, La Paz County, Arizona and Riverside County, California

December 1, 2019

The geologic map of the Blythe 7.5' quadrangle spans about 60 percent of the width of the Holocene floodplain and valley floor of the lower Colorado River and the adjacent lower piedmont on the east side of the Colorado River Valley. This map depicts a composite geologic record of the river’s response to the transition from a natural flow regime to a strictly regulated one created by a series of upstream dams and channelization of much of its length. The floodplain map was developed using archival data sources including notes and maps from early river expeditions, early cadastral and topographical surveys, and a series of historical aerial photographs. The floodplain surface and its underlying young alluvial fill is herein referred to as the Blythe Alluvium, and this report provides the basis for defining it as a formal stratigraphic unit. Along the eastern edge of the map are piedmont deposits intercalated with Pliocene and Pleistocene Colorado River sediments underlying the Blythe Alluvium. The piedmont units include an array of washes and alluvial fans sourced in the Trigo and Dome Rock Mountains. These deposits were divided and mapped based on stratigraphic and geomorphic criteria including relative topographic relationships, and cross-cutting and inset stratigraphic relations among individual piedmont units and with ancestral Colorado River deposits. Varying thicknesses of those units likely exist below the Holocene floodplain, and this report presents those in the form of a lithologic-section of the valley based on available well data and accompanying descriptions.

Publication Year 2019
Title Geologic map of the Blythe 7.5' quadrangle, La Paz County, Arizona and Riverside County, California
Authors Debra Block, Brian F. Gootee, Kyle House, Philip A Pearthree
Publication Type Report
Publication Subtype State or Local Government Series
Series Title Arizona Geological Survey Digital Geologic Map
Series Number DGM-124
Index ID 70206712
Record Source USGS Publications Warehouse
USGS Organization Geology, Minerals, Energy, and Geophysics Science Center