1. Lassen Volcanic
Area: 430 sq km
Best for … volcanic action, scenic drives, snowshoeing
Why go? Lassen is the laidback Golden State at its most inhospitable. All four types of volcano are found here: shield, cinder cone, composite and plug dome; 3,187m active Lassen Peak is one of the largest plugs in the world. Add sizzling fumaroles and burping mudpots, and this is weirdly wonderfully lively terrain.
Most of the main geothermal features can be seen from the main park road. For a closer look, hit the 240km hiking network, which includes the 5km Bumpass Hell path (usually open mid-July- October); this heads into a basin a-bubble with mudpots and steaming pools.
Winter hits hard at Lassen: 15m of snow isn’t unusual. Roads close, so cross-country skiing and snowshoeing are the ways to go; ranger- guided snow-hikes are run for novices.
When to go: Open year-round. Winter/spring access is limited. Mosquitoes are most problematic June-July.