Evolutionary ecology of Arctostaphylos
While this group appears to still be rapidly evolving, fossils go back over 15 million years before the present. That puts them in the middle Miocene, a warm period in North America. The older fossils have all been found in Nevada because in the Miocene, most of California was a shallow sea or a series of volcanic islands featuring a subduction zone the the beginning of the Sierra Nevada.
Arctostaphylos purissima subsp. globosa