California's Sierra Nevada might once have been a literal gold mine, but these days the real mother lode is the promise of adventure. You can explore the South Yuba River State Park for river swim holes and canyons, or head to the Marshall Gold Discovery State Historic Park for 1800s history in Coloma, a charming escape with thrilling outdoor adventures aplenty. Then there's the Plumas-Eureka State Park, which is a bit more of an under-the-radar option that's great for dodging the crowds. Spreading over the mountains around its namesake summit of Eureka Peak, the Plumas-Eureka State Park encompasses a vast swathe of around 7,000 acres. Since the park is set so deep in the mountains, it's easier to drive there from the Reno-Tahoe International Airport than from Sacramento, though both are doable.