city, seat (1850) of Contra Costa county, western California, U.S. It lies on the south shore of Carquinez Strait (between Suisun and San Pablo bays) north of Oakland. It was named for Ignacio Martinez, commandant of the San Francisco presidio and grantee (1829) of the Rancho El Pinole, which was part of the original town site (laid out in 1849 by Colonel William E. Smith). Martinez was originally a trading post, and it became a shipping centre after gold was discovered in the vicinity. In the late 19th century, the city was heavily settled by Italian immigrants, who developed a wine industry there that was later relocated to Napa Valley
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