Geology of National Parks: National Park Service Support Project

Grand Canyon National Park and Parashant National Monument, Northern Arizona: Geologic Maps and Geologic Framework Studies

Overview

The flat layers of rock in Havasu Canyon are travertine terraces formed by the precipitation of Calcium Carbonate. Photograph by George Billingsley.

In the last few years, predictions of severe water shortages in northern Arizona and water rights issues led the National Park Service to identify ground-water investigations in and near Grand Canyon National Park as a high priority for USGS research. The geologic maps produced address a critical resource management question in the Grand Canyon Region: How might increased ground-water development adjacent to the Grand Canyon affect the surface and spring flows? These investigations are being used by the National Park Service, Bureau of Land Management, and U.S. Forest Service.

The image above shows two springs discharging into the Grand Canyon. The water flows from fissures along the same horizon. Faults, fractures, and rock layers strongly influence the flow paths of groundwater. Geologic mapping helps hydrologists to identify the structural features, or geologic framework, controlling that flow. Photograph by George Billingsley.

Springs and seeps discharging from the Redwall-Muav aquifer along the south rim of the Grand Canyon support wildlife and riparian zones. Because water is also a vital component of human activities, the cities of Flagstaff, Williams, and Tusayan, and private entities like Canyon Forest Village are, or have been, considering pumping ground-water from the regional aquifer. The National Park Service has asked USGS for help in assessing whether increased ground-water development adjacent to the Grand Canyon might affect surfaces and spring flows. The members of this project are mapping the rock units and geologic structure of the Grand Canyon region. These physical features underpin the regional groundwater flow system. The geologic mapping investigations are part of an interdisciplinary USGS effort to develop a better understanding of ground-water flow in the region.

A secondary, but nevertheless important, management concern on the Colorado Plateau is the identification of the areas with highest probability that support threatened or endangered plant and animal species. One success of this project so far has been the realization by NPS, USFS, and USGS biologists that the habitats of some rare, threatened, or endangered species, such as the Mexican spotted owl and rare cacti, have geologic controls that can be used to predict species distribution. Project geospatial databases are being combined with biological data for predictive purposes.

USGS geologist George Billingsley conducting a field trip for National Park Service, USGS, and teachers. Photograph by Sue Beard, USGS.

Current and Proposed Investigations

To address the area of greatest need for geologic framework related to regional water management issues, the USGS began new mapping along the south rim of the Grand Canyon. The mapping was requested to provide critical structural information for analysis of geologic controls on groundwater movement and spring discharge. Recharge and discharge areas of the regional aquifer are known to be concentrated along faults and fractures. Geologic mapping of 32 7.5 (1:24,000) minute quadrangles within the Valle 30' x 60' (1:100,000) quadrangle along the south rim of the Grand Canyon is largely completed and GIS production has begun. The proposed new geologic map of the Cameron 30' x 60' (1:100,000) quadrangle is southeast of the Grand Canyon quadrangle and east of the Valle quadrangle.

Grand Canyon Maps

The geologic mapping in the Grand Canyon region fulfills formal requests from the National Park Service, Bureau of Land Management, and US Forest Service. Thus far, project members have produced three new digital geologic maps of the Grand Canyon area: the Grand Canyon 30' x 60' quadrangle, Arizona (Billingsley and Hampton, 2000), Mount Trumbull 30' x 60' quadrangle, Arizona (Billingsley and Wellmeyer, in press), and Peach Springs 30' x 60' quadrangle, Arizona (GIS work in progress). Together they encompass about 6,000 square miles of the Grand Canyon and vicinity.