Contra Costa County
East of the Oakland Hills that border the East Bay, Contra Costa County maintains a very separate culture and lifestyle than its Bay Area neighbors. The area is mostly residential -- although many San Francisco businesses have moved here to avoid high city taxes -- and affluent, and consequently considerably more conservative (by Bay Area standards). The same hills that keep Contra Costa culturally isolated also keep it protected climatically; the area is usually 10-20 degrees Fahrenheit warmer than the Bay.
Highway 24, through the venerable Caldecott Tunnel, is the main entrance to Contra Costa from SF, Oakland and Berkeley. From the south bay (e.g. San Jose) you can take Interstate 680.
BART serves Orinda, Lafayette, Walnut Creek, Pleasant Hill, Concord, and Pittsburg. BART stations have bus service as well. Paratransit (for disabled riders) in Contra Costa is quite good, but you must sign up for it with County Connection LINK and you must reserve your rides in advance. In general, rush hour/commute times in Contra Costa feature traffic jams on the freeways and crowded BART trains.
Mt. Diablo, the tallest mountain of the Diablo range, towers over the county. From the top on a clear day you can see the Sierra Nevada mountains to the east, and Mts. Shasta and Lassen to the north. Entrances to the park are from Walnut Creek and Danville.
The 'mothball fleet', a group of ships mostly from the World War II era, sits just east of Martinez. The ships are being stored rather than dismantled. Among the ships there is the Glomar Explorer, built by Howard Hughes for the US Government to scavenge a sunken Soviet Submarine. The fleet is visible from vista points along Interstate 680 on the north side of the Martinez/Benicia bridge (actually Solano County).
The Ruth Bancroft Garden is a world renown low-water botanical garden in Walnut Creek. The four acre garden has hundreds of succulents and other low-water using plants. It is known particularly for it's Aloes. It is open by appointment only.
Contra Costa has many parks and trails, as well as reservoirs and house museums. Look up the websites for the East Bay Regional Parks System, East Bay MUD (Municipal Utility District = the local water company), designated Open Space areas, Mt. Diablo State Park, etc.
Check out the Lindsay Wildlife Museum in Walnut Creek, where they do wildlife rehabilitation and have live native animals on exhibit along with other more traditional museum exhibits that kids and adults will enjoy.
John Muir's last home is part of a State Park in Martinez, and Shadelands Ranch museum is in Walnut Creek.
There are also many performing arts venues, including the Chronicle Pavilion in Concord.
Downtown Walnut Creek has dozens of restaurants of every description. There are a few familiar chain restaurants, some trendy upscale restaurants, some interesting ethnic places, and a concentration of Starbucks stores, a Peets, and a few smaller, non-chain coffee places. There are also bars and small clubs. Downtown Concord, around Todos Santos Plaza, has some good restaurants, too. Right on the plaza you can find the best Mexican food at Los Gallos, a good Thai place, and there are several more Thai restaurants within a few blocks. There is also a brewpub and a sushi place. On summer Thursday afternoons, there is a farmers' market and live music.