Arizona has many rock shops. Many are in out-of-the-way places, often small, but they hold treasures from the Earth. The Earth’s history is written in the rocks and can be read by those who can interpret geology, geochemistry, and fossils.

The Santa Rita Mountains are of geological importance because they have an almost complete sequence of rocks, from Proterozoic time to the present, a time span of 1,650 million years, in southeastern Arizona. This nearly unbroken sequence of rocks, from every major period of geologic time, has let geologists reconstruct the geologic evolution of southeastern Arizona.

In the Santa Rita’s, faults are abundant structural features; intrusive bodies are numerous, and folds are present in some areas of the mountains. The structural elements, however, have not obliterated the stratigraphic record. The sequence of structural events is decipherable. Furthermore, many events involved in mountain building can be dated using radioisotope techniques due to the presence of igneous rocks. Other estimates of event timing are based on a few faunal ages of the sedimentary rocks. Thus, the Santa Rita Mountains are the key to understanding regional tectonic development.