Although the common perception of Martinez is that of a refinery town, given the view from Highway 680 across the Shell refinery and the strong smell of petroleum that greets visitors coming from the Martinez-Benicia Bridge, the city is in fact largely surrounded by water and regional open space preserves. The Martinez-Benicia Bridge carries Highway 680 across the eastern end of the Carquinez Strait to Solano County.
The city can be defined as a more densely built downtown valley threaded by Alhambra creek and north of Highway 4. Suburban areas stretch south of Highway 4 to join the neighboring city of Pleasant Hill. Unincorporated areas include the rural Alhambra Valley and the Franklin Canyon area.
In early 2007, a group of beavers settled in a section of Alhambra Creek that flows through the city. The beavers and their dam became a local attraction. Because the dam created a potential flood hazard, local officials proposed to remove the beavers. In an emotional city council meeting that was widely attended, residents argued not to remove the beavers. A subcommittee was formed to consider whether this would be possible, and was given 90 days to issue a report to the full council for a vote. During this period, expert Skip Lisle was hired to install a flow device that could regulate dam height and address fears of flooding. The beavers have received national attention, amateur video coverage, a webpage devoted to them, and a new nonprofit organization ("Worth A Dam").