Description:
The Biscuit Flat Quadrangle is located in the northwestern Phoenix metropolitan area, between
Interstate 17 (I-17) and the Agua Fria River (Figure 1). The quadrangle is bounded by latitudes
33°45'00"N and 33°52'30"N, and longitudes 112°07'30"W and 112°15'00"W. Unlike areas to the south
and southeast, the Biscuit Flat area is not (as yet) urbanized. However, knowledge of the distribution and
character of bedrock and surficial deposits may be important to make informed decisions concerning
future management of the land and its resources. Geologic mapping of the Biscuit Flat Quadrangle is
related to other 1 :24,000 scale mapping projects in and around the Phoenix metropolitan area (Figure 1).
Geologic mapping was based on both field observations and interpretation of aerial photographs and soil
surveys. Mapping of Quaternary surficial deposits was initially done by Huckleberry, whereas final
mapping and interpretation of surficial deposits and bedrock areas was completed by Leighty. A limited
amount of unpublished Arizona Geological Survey mapping (by Steve Reynolds and Mike Grubensky for
the Phoenix North 1:100,000 scale geologic map) augmented the new mapping of this report. Also, the
mapping of Tertiary rocks by Jagiello (1987) is locally similar to that of this report. Aerial photographic
coverage of the quadrangle is available from various sources (e.g., U.S.G.S., Bureau of Land
Management, etc.), and includes black-and-white (1:40,000 scale, dated 9-6-92), false-color high-altitude
(dated 5-17-81), and color (1:24,000 scale, dated 10-25-77) photographs. Soil information was compiled
from USDA Maricopa County soil surveys (Hartman, 1977; Camp, 1986). This project was funded by the
Environmental Protection Agency through the State Indoor Radon Grant Program, the U.S. Geological
Survey via the STATEMAP program, and the Arizona Geological Survey.
Geologic map of the Biscuit Flat 7.5' Quadrangle, Maricopa County, Arizona - report and one map sheet, scale 1:24,000.