Evolutionary ecology of Arctostaphylos (Arbutoideae, Ericaceae)
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