Substrate controlled endemism IS the California flora: in one word; serpentine! A secondary “hot spot” in our flora is limestone and/or marble. Be it a big white flowered shrub, Neviusia, or a Heterotheca monarchensis, calcareous substrata are invariably worthy of exploration for new novelties or new records.
In the Sierra, limestone and or marble occurs as isolated, small rock masses, often these do not get mapped at the 1:250,000 scale of the state geologic maps. A systematic survey of these 'islands' is needed.
A calcareous site worthy of visitation is Marble Cone, in the Middle Fork Feather River. At least based on CCH specimen records with coordinates, no collector has been in the vicinity. Access seems, from the topographic maps at least, is uncertain, but 4WD roads get within about a mile upcanyon, or a trail about the same distance downcanyon.
Someone, go yonder.