The lands west of Alvarado have been used for salt making since the 1860's. Different companies came and went over the years. In the 1910's, Continental Salt Works had a factory 1.5 miles west of Alvarado, making 200 tons daily of salt and employing 30 workers. In 1924, the Continental Salt Works merged with Leslie Salt, and the salt works near Alvarado continued to operate.
In November, 1935, the salt works burned to the ground. The November 7 issue of the Oakland Tribune provides the details:
Fire of an undetermined origin completely destroyed the plant of the Continental Salt Company on San Francisco Bay a mile west of Alvarado yesterday, with damage approximating $100,000. The “Haze M,” a $14,000 tugboat and a $7,000 barge belonging to the Miller Launch Company of San Francisco, beached by low tide, were also destroyed, as were the transformer poles and equipment of the Pacific Gas & Electric Company.
The plant, which handled about 30,000 tons of salt a year is one of two operated by the Leslie California Salt Company. A third plant is located at Mt. Eden. The 25 men employed at the Continental plant will be put to work at other branches.
Rolly Montalbo, captain of the “Hazel M” stated that it was impossible to save the boat and barge as low tide had left them stuck in the mud. Crude salt transported in 150-ton loads from the plant to the San Francisco waterfront is used for salting fish, curing hides, etc.
Some of the employees have been connected with the salts works for more than thirty years, among them William Johnson who in the early days operated freight boat between Alvarado and San Francisco.