The Mousley Museum is a small free natural history museum in downtown Yucaipa, founded by a local family and now run by volunteers. The collection is wide — California minerals and fossils in the front rooms, taxidermy of local desert species, Native American baskets, seashells, and one curiously substantial dinosaur skeleton casting in the main hall.
It is the kind of small-town museum where the docent will spend an hour with you if you let them. Children with any interest in rocks or bones will probably want to stay longer than you do. Opening hours are limited — usually a few afternoons a week — and admission is free, though donations are welcome.