When the ponds around this area were first built, producing salt by solar evaporation required intense labor and a great deal of time. Workers moved seawater from San Francisco Bay, with only 2.5% salt content, through a series of evaporation ponds to concentrate it to the point of crystallization, a process that took almost five years. In the late 1800s, laborers used shovels, wheelbarrows, and carts to move crystallized salt out of the evaporation ponds, and in later years mechanized equipment and narrow-gauge railways helped speed up harvesting. In 1901, Japanese immigrants made up most of the Oliver Salt Company's harvest-time employees, but segregated treatment, harsh working conditions, and the company's reluctance to raise wages to $1.35 a day led many of these workers to leave for higher-paid agricultural employment.