Both urban areas and low, rugged mountains and ridges surrounding San Francisco are captured in this photograph. Two northwest-southeast-trending faults are discernible—Hayward Fault, bordering the urban area east of San Francisco Bay, and San Andreas Fault, crossing the mid-San Francisco Peninsula before dipping beneath the Pacific Ocean and surfacing again northwest of Golden Gate Bridge. Five major bridges connect Bay Area communities, and two highway arteries connect the densely populated Bay Area with the valley to the east and the communities of Walnut Creek, Concord, and Livermore. The colors along the southern edge of the bay are produced by the growth of algae in salt pans of varying degrees of salinity. Sediment plumes are visible in San Francisco Bay and the Pacific waters west of the Golden Gate Bridge.