Directions to the site:
* From Hwy 101, drive approx. 2 mile north of Orick to Davison Road and turn left.
* Follow through Elk Meadow and onto dirt road (motorhomes and trailers are not allowed on this road). Follow this spectacular scenic drive for 6 miles until you reach the Gold Bluffs Beach kiosk. Pay the $8.00 day use fee (cash or check only). California State Park and National Park Service passes are accepted.
* Follow the road along the beach for another 2 miles until the reaching the coords for the parking lot.
Most of the area is underlain by rocks of the Franciscan Formation (also called a Group, Series, assemblage, or complex). The Franciscan is composed of greywacke, shale, altered volcanic rocks, chert, some limestones and metamorphic rocks including greenstone (altered submarine volcanics), glaucophane schist, chlorite schist and serpentinized peridotite. The Franciscan Formation is over 50,000 feet thick and no top or bottom has been recognized. The age of the Franciscan extends from Upper Jurassic to Upper Cretaceous (Bailey, et. al, 1964). Much of the Franciscan assemblage consists of rock that has been sheared and lifted from the ocean floor as a result of the plate action along the Cascadia subduction zone.
The Franciscan has been subdivided into various units according to lithology, mineralogy, and degree of metamorphism. In the Redwood Creek area southeast of Orick, CA, the Franciscan is divided into four named units (from oldest to youngest): Redwood Creek schist, Snow Camp Mountain unit (west of Redwood Creek), Coyote Creek unit, and Lacks Creek unit (both east of Redwood Creek). There are other unnamed units including the metamorphosed sandstone and mudstone of the Grogan Fault Zone and sandstone and mudstone units above the Lacks Creek unit (Hardin, et al, 1981).
The Redwood Creek schist consists of two major rock types: metasedimentary rocks consisting of lightcolored, fine-grained schist and phyllite, and metavolcanic rocks which include massive greenstone and fine-grained, foliated metavolcanics (Cashman, et. al., 1986). The Snow Camp Mountain unit consists of bedded graywacke and mélange (a mixture of various sized particles and various rock types). The Coyote Creek is an incoherent unit consisting of mudstone with some sandstone and blocks of greenstone and chert (Harden, et al, 1981).The Lacks Creek unit is a turbidite deposit consisting of mostly coherent sandstone with interbedded mudstone and sandstone. The sandstone may be massive forming steep slope and prominent ridges.
Coastal plain sediments are present to the north of Redwood Creek designated either the Prairie Creek Formation or the Gold Bluffs Formation. These are unconsolidated to weakly consolidated sand, silts, and gravels. The oldest sediments contain fragments of Pliocene plant fossils (Harden, et al, 1981). Youngest deposits are stream terrace alluvium, landslide deposits, and modern floodplain and overbank deposits.
Geological hazards have a very high priority with the park and most are associated with fluvial processes and seismic activity discussed above. Landslides are natural occurrences on steep slopes underlain by Franciscan rocks, but logging and road construction have accelerated the downhill movement of slope material. This has also increased sedimentation in stream and the potential for rockfalls. The channelization of streams allows large slugs of sediment to move rapidly (and more destructively) downstream.
Large dormant and paleo-landslides are being mapped, but the smaller features associated with specific surface disturbances are also of great concern. Erosional and landslide hazards on Redwood Creek were mapped by Steve Coleman in 1973. A 1978 coastal landslide map is available. At present there are no facilities located on or near active landslides. Campgrounds are located on floodplains which may be at increased risk from flooding and mudflows. In 1997, storm events triggered about 400 landslides, taking out roads and culverts. Most event occur during the winter when there is lower visitation.
Road restoration has been a major undertaking at the park. This effort has restored many of the old logging roads and reduced landslide activity in those areas. However, most roads open to visitor traffic are gravel and subject to erosion.
To log this cache, go to the above coordinates for required information. Then e-mail me your answers. (Do NOT post the answers or the option in your log.) Also, posting a picture of you or your group would be appreciated but not required.
PLEASE NOTE: ALL LOGS WHO DO NOT SEND THE REQUIRED ANSWERS WILL BE DELETED WITHOUT WARNING.
1. In your opinion, what geologic material are the bluffs primarily composed of?
2. There have been landslides along these bluffs in recent years. What do you think caused the most recent landslide south of the posted coordinates about a half mile, ( Man (making the road) or nature (weather and area quakes etc.) Why?
3. What color are the bluffs?
4. Optional: Post a picture of yourself and/or your group keeping the main topic of this Earthcache out of view.
Thanks for visiting my Earthcache!!