| The left (west) side of the Highway 101 roadcut is composed of the
interbedded sandstones and shales. They are underlain by by hard, silica
rich rocks that we will observe as we continue our trip (just above the
Sausalito road sign). And at bottom of the sequence, the core of the Spencer
Ave. road cut is in former volcanic rocks erupted under the ocean. The
rocks are tilted from upper right to lower left. This sequence has been
lifted from the deep ocean floor essentially intact. The resistant layer
without vegetation that caps the hill beyond the first roadcut is the silica
rich layer in the sequence. |
