Geologic Setting The geologic setting of Westline Drive in Daly City is underlain by greenstone (metamorphosed ultramafic basalts) of the Cretaceous Franciscan Complex, friable to weak sedimentary rocks of the Merced Formation (deposited in the Pliocene), and serpentine. These rocks are covered by weakly cemented marine terrace deposits, landslide debris, colluvuim (slope wash deposits), and sand dunes deposits. A prominent escarpment north of Westline Drive defines the southern boundary of Mussel Rock Landslide Complex, an approximately nine million cubic yard mass movement that occupies the open space at Mussel Rock (Jacob Associates 1998).
