Although the common perception of Martinez is that of a refinery town, given the view from Highway 680 across the Shell refinery from the Benicia–Martinez 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.