The earthen dam that forms Lake Lagunitas was built in 1872 for $95,000 by William T. Coleman’s Marin County Water Company. Coleman established his company to facilitate the sale of real estate in his private development of Magnolia Park (now the Dominican neighborhood in San Rafael) and to supply other potential development in the San Rafael area and the state prison at San Quentin.
The dam was designed by Herman Schussler, chief engineer of the Spring Valley Water Company in San Francisco and built in less than four months by Chinese workers who were paid just $20 per month. The crest of the dam was 480 feet in length with a width along the crest of 20 feet. Capacity was estimated at 150,000 gallons, enough to last San Rafael for two years.
In December 1877, Marin County’s first telephone line was completed between the Marin County Water Company’s office on C Street in San Rafael and the lake keeper’s house about 100 yards below the dam (the cottage was destroyed by fire in 1925). The company built the 6 miles of line and rented the phone equipment for $5 per month.
The dam was raised two feet in 1912 (the same year MMWD was chartered) and another two feet in 1935 to its current capacity of 350 acre-feet or approximately 114 million gallons.
MMWD came into possession of the reservoir and surrounding watershed lands in 1916.