Mount Diablo. Here's a closer view taken from the Carquinez Straight. If you click to enlarge, you'll see the C&H Sugar mill behind the bridge on the right. In doing so, you'll also see that this is actually two bridges. The eastern most span carries east-bound traffic on Interstate 80, while the one in the foreground carries the westbound traffic.
The Carquinez bridge lies between Crockett on the south and Vallejo on the north. The original Carquinez bridge predates either the Golden Gate Bridge or the San Francisco-Oakland Bay Bridge.
Here's a snippet from Wikipedia about the Carquinez Bridge.