Hmm. That depends on what you want it to be. If you’re doing a National Parks land, then you could either do the 1940s/50s family road trip theme seen presently in Grizzly Peak, or you could go earlier to the days of John Muir when the Parks were first established. Or if the California Goldrush is what’s most interesting, set the land circa 1849 and include a somewhat Discovery Bay version of San Francisco.
Hope this helps.