The San Pedro River of southeastern Arizona is the last major undammed river in Arizona. In an effort to better understand the nature of groundwater flow in the vicinity of San Pedro and its tributaries, the Arizona Dept. of Water Resources contracted with AZGS to conduct detailed geologic mapping of Pleistocene and Holocene deposits adjacent to the river and its major tributaries. This picture illustrates the distribution of Pleistocene tributary fan deposits, eroded basin fill, and Holocene river deposits. The results of that study, which includes a 78-page report and six map sheets, were published in 2009 (http://repository.azgs.az.gov/uri_gin/azgs/dlio/799). The GIS database is available for the six map sheets. A second report, Geology and Geomorphology of the San Pedro River, Southeastern Arizona, by Pearthree and Cook was released in 2015. (http://repository.azgs.az.gov/uri_gin/azgs/dlio/1633).