Getting There
The Cottonwood Trailhead and Horseshoe Meadows are easily accessible from both the Los Angeles and Bay Area locations. If you do head into Lone Pine you can access Horseshoe Meadows Road from Whitney Portal Road in Lone Pine.
From Los Angeles Horseshoe Meadows is a quick 4 hour drive up Highway 395. If you're not interested in stopping in Lone Pine make the left on Lubken Canyon Road (just before you enter Lone Pine). Follow Lubken Canyon Road to Horseshoe Meadows Road and follow that up the hill and to the various walk in campsites (10,000') at the trail head.
From the San Francisco Bay Area this is a LONG 7 hour drive from most locations, but in my opinion very much worth it. For most of the Bay Area this drive will take you South, down Interstate 5 and Highway 58 through Bakersfield. Sierrabackpack.com doesn't recommend Highway 178 through Isabella as you could get back up behind RV's and because it's a windy road it tends to be slower. Instead stay on Highway 58 through Tehachapi and connect with Highway 14 just north of Mojave. Follow Highway 14 north where it intersects with Highway 395 and follow this north to Lubken Canyon Road (just before Lone Pine). Make a Left on Lubken and a second left (after a mile or two) onto Horseshoe Meadows Road. Follow Horseshoe Meadows road up the hill and to the various walk in campsites (10,000') at the trail head.
For Northern Bay Area Locations (Sonoma, Napa, and locales north) - a 7 hour+ drive, the best route is via Interstate 50 to Highway 89 in Meyers (south of Lake Tahoe). Follow Highway 89 to connect with Highway 395 and follow 395 south to Lone Pine. Exit (right) in Lone Pine on Whitney Portal Road. Follow Whitney Portal a mile+ to Horseshoe Meadows Road, make a left and follow that up the hill and to the various walk in campsites (10,000') at the trail head.