Tourmaline Beach Geology 101 Field Lab – Fall 2010

Mesa College

Dates: Friday, December 10^th @ 9:15 AM

Where: Meet at Tourmaline Beach Park – West end of parking lot next to bathrooms

Note: There are fieldtrip guide maps and directions.

How to Get There:

Directions:

	Follow I-5 south to Pacific Beach.
	Take the Grand/Garnet/Balboa Ave exit.
	Turn right (west) on Garnet; stay on Garnet all the way to Mission Blvd.
	Turn right (north) on Mission Blvd. Then turn left onto La Jolla Blvd. Almost immediately, turn left onto Tourmaline Street.
	Follow Tourmaline Street down the hill and park anywhere you can along the roadside.  If you're feeling lucky, try the beach parking lot.
	Once you've parked, walk down the hill, to Tourmaline Beach.

For an in-depth description of this beach and how top get there go to:

http://entertainment.signonsandiego.com/places/tourmaline-surfing-park/#

Self-Transportation:

Carpooling with your fellow students is highly recommended.

Public Transit:

Call San Diego Transit at (619) 233-3004 for buses that serve this beach.

Parking:

A 30 space parking lot (3 disabled spaces) can be found at Tourmaline Beach Park. In summer, this lot fills to capacity by mid-day. Limited on street parking may be available.

How Long Will the Trip Last?: The trip will probably take about 2 to 3 hours to complete.

Cancellation due to Weather: The field trip will be cancelled if it rains.

Purpose: To familiarize students with the coastal geology of San Diego County: 1) better understand the concepts concerning shoreline processes and geomorphology, 2) tectonics and recent faulting, 3) depositional and erosional environments and local stratigraphy, and 4) the geologic history of San Diego County.

Lab Activities: Observe, Study, Measure, and Discuss the nature of deposition and erosion of the beaches and bluffs, coastal geology, and recent faulting within coastal San Diego.

Field Assignment: Students will be required to complete a field trip handout, which includes answering fill-in questions, and writing a short reflection on the field trip experience.

The worksheet that we will complete during this field excursion can be found at this link:

http://www.terrasonics.com/geolab_fieldtrip2_worksheet.htm

What to Bring: Students should bring a clipboard, notebook, writing tools, a ruler, camera, water, sunscreen, and a surfed-out attitude.

What to Wear: Loose, comfortable clothes (T-shirt and shorts is good) along with a hat and sweatshirt or windbreaker. Beach weather may could range from sunny and warm to overcast and cool. So it is a good idea to be prepared either way.

How to Prepare for Fieldwork: Carefully study the information and figures found below before the day of the fieldtrip:

Geologic Background of Tourmaline Surf Park, San Diego, California

If we travel approximately 10 miles west of campus to the coast - north of Mission Beach - to Tourmaline Beach we find rocks exposed along the sea cliffs. Because of the strike and dip of these rocks a traverse northward along the base of the cliffs provides exposures of progressively older and older rocks. The oldest rocks are found at the base of the cliffs are at False Point. Although these rocks are all sedimentary, they have different lithologies, have different names, and represent somewhat different time intervals than those around the campus area. Using similar techniques of geologic mapping the relationships of these rocks are known. An important task for geologists is to determine how the rocks from these two areas are related. This technique is known as stratigraphic correlation.

Geology Map of Area

Stratigraphic Column

Tourmaline Beach - Meosozic Time

The oldest rocks exposed along the cliffs at Tourmaline Beach are to the north end of the beach at False Point. These are sedimentary rocks that are mostly conglomerate and some very coarse grained sandstone called the Cabrillo Formation. These rocks were probably deposited in shallow marine to beach conditions. Although few fossils have been found in the Cabrillo, fossils in associated formations provide evidence of a Cretaceous age, but somewhat younger (perhaps 40 million years younger) than that of the Santiago Peak Formation exposed a bit further inland.

Tourmaline Beach - Cenozoic Time

Cenozoic rocks exposed at Tourmaline Beach are sedimentary rocks that include conglomerate, sandstone, and mudrock. The oldest of these are pebble to cobble conglomerate and sandstone of the Mt. Soledad Formation. These rocks were deposited as channel fill in beach environments. Conformably above the Mt. Soledad Formation are mudstone and siltstone of the Scripps Formation. These rocks were deposited in environments ranging from tidal flat to submarine fan. Fossils in these and laterally equivalent formations in other local areas indicate that both formations are of Early Cenozoic age (Eocene), but are slightly older than those at SDSU.

Overlying these Eocene rocks are sedimentary rocks consisting of conglomerate and fine grained sandstone called the San Diego Formation. The conglomerate has cobble sized clasts and occurs at the base of the formation. The remainder of the formation consists of sandstone. These rocks are not well cemented and tend to crumble easily. They were formed in intertidal and beach environments. Fossils are abundant in some layers of the formation, and indicate an age of Quaternary (Pliocene).

The youngest rocks at Tourmaline Beach are terrace deposits that are probably of Pleistocene age. They consist of mud, sand, pebbles and cobbles that are weakly cemented together and tend to erode easily. Not a great place to build a house! The stratigraphic relationships of these rocks are illustrated below.

Richard Miller - SDSU - Author