California

California State Parks prohibit removing or disturbing any geological or paleontological feature (California Code of Regulations Title 14, §4307), and the ban includes beaches inside state parks — so the classic Capitola and Santa Cruz shell beds and the Mount Diablo area are look-only. State beaches outside park units are managed by the State Lands Commission and local authorities; loose beach finds are widely tolerated, but there is no explicit right to collect.

BLM land in the Mojave and the eastern Sierra follows the federal casual-collecting rule for common invertebrates and plants, and the Forest Service rule applies in national forests; petrified wood is under the free-use rule. The Marble Mountains trilobite beds are BLM land (personal use only) with a nearby Wilderness Area closed to collecting.

Sharktooth Hill near Bakersfield — the Miocene Round Mountain Silt, source of Carcharocles teeth, whale and sea lion bone — is private ranch land: the Ernst Quarries and other operators sell digging by the day, and what you find is yours to keep and sell with the dig receipt as provenance.

California's ivory and rhinoceros horn law (Fish and Game Code §2022) prohibits sale of ivory from elephant, hippopotamus, mammoth, mastodon, walrus, warthog, whale and narwhal, with narrow antique (under 5 % by volume, pre-1975) and musical-instrument exceptions; mammoth ivory is expressly included, and possession at a sale venue is evidence of intent. Anything ivory offered at a California show or shipped into the state is a problem.