The first residents of what is now San Leandro were Indians. They arrived at least 3,000 years ago, judging by the age of oyster shell mounds they left behind. The area was explored by the Spanish in 1772, and their first settlement was established by Don Joaquin Estudillo in 1837. In 1842, the Spanish government granted him ownership of Rancho San Leandro, which included about 6,832 acres. Part of the city area also was included in land granted to Don Luis Maria Peralta in 1820.

The Gold Rush brought many newcomers to the area. Miners who failed to make their fortunes in the gold fields turned to farming in San Leandro to provide fruit and vegetables for San Francisco’s growing population. San Leandro served as the seat of government in Alameda County from 1856 until 1868, when a major earthquake knocked down the courthouse. The area recovered from the quake, continued to grow, and incorporated on March 21, 1872.

Industrialization began in the 1880s, when an early San Leandran, Daniel Best, built an automobile or "horseless carriage." Later, he manufactured farm tractors, laying the groundwork for what would become the Caterpillar Tractor Co. As industry flourished, the city grew, reaching a population of 11,455 in 1930. The population hit 27,542 in 1950. It is now more than 275 percent higher.

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