FIELD TRIP Name___________________________

April 16, 2016

1. Leave: 9:00 A.M., 5th and San Salvador Streets

2. Bring: (a) pencil & notebook (b) hand lens (c) tennis shoes or boots (d) warm clothes (e) lunch & water

3. To see: (a) San Andreas fault (b) Seal Cove fault straddled by new houses (c) syncline at Moss Beach with angular unconformity (d) Purisima Formation with fossils, boulders, etc. (e) tide pool life and sediment (f) geological history of Montara Beach (from road to point at south end of beach)

4. Home: 4:00 P.M.

- Depart School at 9:00 am - Drive for 50 minutes to a lookout over the San Andreas Fault - Pull into a lookout area around 9:50 am.

STOP #1. Crystal Springs Reservoir - 1st vista point north of Edgewood Road. This reservoir occupies a portion of the San Andreas fault zone, here quite wide. About 4 m (13 ft) of right-lateral slip was recorded (by offset fences, dams, etc.) in this area during the 1906 San Francisco earthquake. Franciscan rocks (Cretaceous accretionary complex) crop out just northeast of the fault, whereas Cretaceous plutonic rocks lie in the area to the southwest. This contrast of lithologies is the basis for interpretations of up to 320 km (200 mi) of cumulative displacement along the San Andreas fault.

- Leave lookout area at around 10:30 am. - Drive for 40 minutes to Half Moon Bay Airport - Note that when we cross the water while on Highway 92, we are directly over the San Andreas

Fault. - Arrive at Half Moon Bay Airport (Stop #2) at approximately 11:15 am.

STOP #2. Half Moon Bay Airport. This flat coastal area is a 100,000-year-old marine terrace recording a relatively higher stand of the sea. Note the old wave-cut cliffs to the east and partly dissected higher terraces. The higher elevation of this same terrace west of the airport has been caused by uplift on the Seal Cove fault.

- Leave airport around 11:30 am - Drive for about 10 minutes to Montara Beach - 11:50: Lunch at Montara Beach

STOP #3. Montara Beach. Study the rocks exposed from the road southward to the point. Divide the sequence into several distinctive lithologic units and indicate their relative ages. Look for faults, unconformities, etc. Start a list of the sequence of geologic events represented on the last page of the handout. Be specific and use your knowledge from lecture and lab to interpret the geology here.

- Leave Montara beach around 1:20 - Drive for about 5 minutes to Moss Beach

STOP #4. Moss Beach. FINAL STOP: NOTE - THIS IS A STATE PRESERVE - COLLECTION OF ROCKS OR TIDEPOOL ANIMALS OR PLANTS WITHOUT A PERMIT IS STRICTLY PROHIBITED. The Seal Cove fault extends out to sea beneath the boulder pile at the south end of the beach. A syncline in the Purisima Formation (Pliocene in age) plunges seaward. A shallow-water fauna and large granite boulders are set in a fine-grained sandstone matrix.

- Leave Moss Beach at 2:45 - Drive for 1 hour back to school. - Arrive back at school between 3:30 and 4:00

Name _______________________

ASSIGNMENT

Montara Beach Geologic History

1. Study the area on Montara Beach from the bus to the south end of the beach.

2. First determine which are the oldest rocks and then divide the rocks into several stratigraphic units (about 5) on the basis of different colors, textures, composition, etc.

3. List in order the sequence of geologic events that these rock units record. The granitic rocks are Cretaceous in age.

Sequence of Geological Events at Montara Beach (put the oldest event at the bottom)