By 1957, the school age population of the Tamalpais Union High School District had grown too large for Tamalpais High School and Sir Francis Drake High School to accommodate. With the pressure of students coming in from elementary schools from Sausalito to Belvedere to Ross, voters chose to create a new school, and chosen for its site was the marshy area that extended east from the centrally located town of Larkspur to U.S. Route 101, an area that townspeople had called "the slough" since Larkspur was settled. The importance of wetlands was not yet widely appreciated (this was the era right before Save the Bay was founded), and the land was seen as "waste." Beginning in early 1957, a large section of the marsh was flattened and filled, two roads were cut through from Magnolia Avenue out to the new school, and school buildings were constructed, along with a playing field and parking lot.