From Tom Stienstra's Outdoor Vacation Awards:

Best chance at vertigo:
At the end of the 2.5-mile hike to the 8,587-foot Sierra Buttes in Tahoe National Forest, you climb three exposed stairways that jut out over the canyon. A lookout station is perched on a crag and you walk atop an open-grated deck that feels like you are walking on air. The only sensation I've felt that is more dizzying .....

Read more, and about many other interesting places in California: http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2010/07/29/SP0H1EK90R.DTL&feed=rss.tstienstra#ixzz0y9nrLGMB