If you’re looking for fall in California, you can’t beat the Eastern Sierras and the town of Mammoth Lakes. When to Visit: If you’re looking for fall in California, you can’t beat the Eastern Sierras and the town of Mammoth Lakes. When the aspens turn, entire hillsides come alive in a blaze of warm gold. For a festive, fall weekend, I recommend visiting in mid-September or October. If you want to be sure to plan your trip around peak foliage, keep an eye on the helpful ‘Fall