Road log for southern Santa Rita Mountains, Santa Cruz and Pima Counties, Arizona

Geologic mapping of the Mount Wrightson quadrangle has been completed recently by the U.S. Geological Survey. As a result, I am able to present a summary (table 1) of the rocks exposed and to indicate their ages and relations with each other. The Mesozoic rocks are emphasized because the local geologic record of this era is more complete in the southern part of the Santa Rita Mountains than elsewhere in southern Arizona. For example, there is evidence to indicate that about 10,000 feet of volcanics (including pillow lava), eolian sandstone, and possibly even red beds was deposited during Triassic time and that these rocks were intruded by a monzonite stock before the end of that period. It is hoped that release of the data at this time, prior to the final publication by the U.S. Geological Survey, will stimulate in the geological community of southern Arizona a timely interest in some of the complex problems of the Mesozoic tectonic history. Solutions to these problems may suggest new approaches to minerals exploration in this region.