The League lobbied and assisted with fundraising to stop plans to fill and dredge a 69-acre salt marsh south of the mouth of Corte Madera Creek. In 1976 the State of California became owner of the marsh, which is now part of the Corte Madera Marsh Ecological Reserve under management of the State Department of Fish and Game.

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.