In 1943 the League contributed $15,000, which the County matched, to purchase the 190-acre Shell Beach as a county park. At the time the State could only purchase parkland if half the purchase funds came from non-state sources, so MCL persuaded the County to give Shell Beach plus matching funds of $26,000 to the State in 1948. The State matched the County’s contribution of land and funds and purchased an 840-acre parcel of beach and forest north of Shell Beach for $150.000. In 1951 the area, including five sandy beaches, two miles of waterfront and acres of Bishop Pine, became Tomales Bay State Park. MCL had contributed $25,000 in cash and thousands of volunteer hours to the effort.

MCL continues to work on preserving important natural features of Marin. Projects have included the San Rafael Shoreline, Corte Madera marshes, Bahia, Rush Creek in Novato, Bel Marin Keys and other creeks, wetlands and ridges.