Geologic Mapping of the Lower Colorado River System

Science Center Objects

This is a comprehensive scientific investigation of the geologic history and framework of the lower Colorado River. We are using geologic mapping in combination with stratigraphic, geochronologic, and geophysical studies to develop a holistic understanding of the river’s origin, the structural history of the landscape through which it flows, and the stratigraphic and geomorphic consequences of the river’s changes in response to long and short-term changes in regional tectonics and climate.

An illuminated steep bluff face in the desert that reveals complexly deformed and folded sedimentary strata.

Deformed sediment of the Bouse Formation in Chemehuevi Valley, California. Complex deformation is a likely consequence of subaqueous mass wasting of part of a growing delta of the Colorado River.

(Credit: P. Kyle House. Public domain.)

Science Issue and Relevance: 

The lower Colorado River study area includes one of the world’s most iconic landscapes (Grand Canyon) and embodies a water resource that is essential to the water and electric power requirements of more than 40 Million people in the southwestern United States. 

  • There is wide-reaching cultural relevance in simply explaining the Grand Canyon, and we can’t begin to do that without understanding how the lower river corridor evolved.
  • Regional crustal extension and associated sedimentary deposits created the characteristics of modern-day aquifers 
  • Detailed geologic mapping investigations build knowledge and provide deep insights into geologic processes and related natural hazards endemic to the lower Colorado River.
  • Maps of the lower Colorado River will be integrated into National geologic map datasets.

Methodology to Address Issue: 

Geologic mapping is the foundational method employed in this project. Mapping is a means of documenting, synthesizing and portraying scientific observations and interpretations of geologic deposits that record important episodes and timing of geologic activity. Our project is based primarily on surficial geologic mapping and regional-scale geologic maps but, will also conduct bedrock mapping and related structural studies. Our workflow involves characterizing and portraying a complex stratigraphic record at intermediate scale (e.g., 1:100,000). This process includes new geologic mapping in addition to compilation and refinement of existing maps, using a common stratigraphic nomenclature. These efforts are rely on modern GIS technology.

Oblique view of flat surface mantled with tightly packed, well-rounded cobbles & pebbles, shiny reddish-brown to black surface

Linear tracts and small patches of well rounded and varnished pebbles and cobbles mark the traces of ancient channels, bars, and floodplain terraces of the lower Colorado River. Extremely long durations of exposure to the desert environment transform the surfaces of these deposits to flat, and tightly packed pavements of spectacularly discolored and varnished river rocks.

(Credit: P. Kyle House, USGS. Public domain.)

Geochronologic studies will focus on the ages of key Colorado River strata and underlying bedrock units and geologic structures that have influenced the river’s evolution. Structural and stratigraphic analysis of the geologic framework of the basins that hold voluminous water resources will be critically important in coming years and decades. 

Aerial view of a strongly discolored river in a deep and rugged canyon. Blue sky and scattered clouds above the canyon

Summer flash-floods can introduce large amounts, of fine reddish-orange sediment to the Colorado River with spectacular results

(Credit: Ryan Crow, USGS. Public domain.)