Climbing

• Supertopo.com – The main forum for California’s climbing community
• Mountainproject.com – Crowdsourced guidebook, with good mobile app
• Summitpost.org – Competitor to Mountainproject; skewed towards less technical routes

Backpacking

• Postholer.com – Trail blogs, maps, and more
• Yogi’s Guides – Guidebooks for long-distance hiking

Mountaineering

• Freedom of the Hills – Get a copy and read it compulsively.

Backcountry Skiing

• Bob Skiing’s guidebook list
• Tahoebackcountry.net – Random assortment of trip reports
• Skitahoebackcountry.com – Good basic guidebook to the Tahoe area
• Backcountryskitours.com – Cross-country ski tours
• Skimolife.com – Training and skim mountaineering trip reports
• Andy Dorais’ Blog – Inspiration for ultralight ski mountaineering