 Mare Island refers to an island which is part of Vallejo. It is said  to be names after a prized white mare owned by Gen. Mariano  Guadalupe Vallejo. On an occasion when a number of the Generals  horses were being ferried across the Strait from the Contra Costa  shore to Benicia, the crude barge capsized. Some of the horses swam  ashore, others drowned, and the white mare disappeared. It is  recorded that many weeks afterward, the white mare was discovered  grazing on the hillside of the island across the channel from  Vallejo. From that day, the island was known as "Mares Island,"  shortened to Mare Island.