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Brooks Island is a , mostly flat strip of land extending from a round hill which peaks at in San Francisco Bay, located just south of the Richmond Inner Harbor in Richmond, California.〔〔〔(Brooks Island profile ), East Bay Regional Parks District website, retrieved August 3, 2007〕 ==Geography and geology== The rock that forms the main peak of the island is radiolarian chert underlain by limestone and graywacke sandstone. All these rocks are part of the Franciscan Assemblage, the same range as Albany Hill, 3 miles south, and the Coyote Hills, 25 miles south in Hayward.〔 This Franciscan formation is derived from sediments laid down in the sea west of San Francisco during the Late Jurassic and Cretaceous (150-66 million years ago) and then scraped off onto the edge of the North American plate during the subduction of the Farallon plate.〔 The main portion of the island covers an area of approximately .〔 A short distance from the southwest coast of the main island is Bird Rock or Bird Island. The sandspit that extends for about two miles west of the main island formed along a breakwater that was installed in the 1920s to preserve a deepwater channel to the Richmond Inner Harbor.〔 During the last ice age San Francisco Bay was a valley, and Brooks Island was just one hill of many along its western slope. As sea level rose, the valley was flooded and Brooks Island was cut off from the rest of the East Bay.〔 Although the island is quite small, there is a permanent spring, which is used by the caretakers as a water source.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Brooks Island」の詳細全文を読む スポンサード リンク
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