Using geological and topographic maps, existing studies, and in-field rock formation analysis, geological points of interest along the trails in Charmlee Park were identified and existing maps of the area were corroborated. Points of interest were photographed and their coordinates were found using Garmin GPS units for use in visitor information documents. The information documents will serve to promote interest in the geological history of the Santa Monica Mountains and Charmlee Park. The geology of the park consists mainly of two large formations, the Topanga and Vaqueros marine sandstone formations of the Early to Middle Miocene. Several points of contact between these formations, evidence of mountain building and faulting, macroscopic marine fossils, and a large fault are visible from the trails in the park. In addition, a large syncline lies under the Meadow area. All of these are included in the mapped points of interest found.

Charmlee Park is located northwest of Malibu, on the coast of California near Point Dume. It used to be owned by the County of Los Angeles but it was recently acquired by the City of Malibu. The City was eager to learn more about the natural resources of the park and also to improve the ability of the park staff to make information about these resources available to visitors. Together with a geography team from CSULB, our job was to make a digital map of the park's geographical and geological features that could be displayed on the internet. To do this, we first did research in the library to find existing information about the area. We used geological maps of the Point Dume Quadrangle, which is next to the park, and the Triunfo Pass Quadrangle, in which the park is located, to learn more about the geology of the park and to find specific points to investigate in the field.

We mapped outcrops and trails using Garmin GPS units, as well as taking photos of the points we marked. We worked in the computer lab downloading these points and trails into a Geographical Information System (GIS) program called ArcView. The program allowed us to superimpose the points onto a topographical map of Charmlee. In addition, we described the rock formations, geology and processes of the points of interest on our maps of the area

Tectonic Regions

Charmlee Park lies near the edge of the Pacific tectonic plate, right on the coast of the Pacific Ocean and relatively close to the North American Plate, on which the eastern half of California lies. Southern California in particular has been divided into several tectonic regions, most importantly, the Mohave Desert, Coast Ranges, Peninsular Ranges and the Western, Central, and Eastern Transverse Ranges (Fig. 1) (SCAMP, 2003).

Charmlee Park is in the Western Transverse Ranges Province, which encompasses the Channel Islands, the Santa Ynez Mountains, Ventura Basin and Simi Valley, and the Santa Monica Mountains, where Charmlee Park lies. These ranges are interesting because they lie in an east-west direction, while the Coast and Peninsular Ranges lie roughly parallel to the coast of California. The reason for this is that the north-south motion of the two large plates (Pacific and North American), which meet at the San Andreas Fault, has caused small pieces or "blocks" to break off, and over time, these blocks rotate. The Transverse Ranges used to be parallel to the coast like the Coast and Peninsular Ranges, but they have been turned to their present east-west position (Ramírez- Herrera, personal communication, 2003).

Sea Level Changes

Southern California has undergone major changes in the sea level over the last 180 million years, especially since the beginning of the Eocene epoch, where the sea level changed directions several times in the space of 19 million years and continued to do so at a similar rate. The area around Charmlee Park, however, remained underwater for much of this time, not becoming permanently exposed until the Upper Pliocene, about 1 to 4 million years ago (Fig.2) (Reed and Hollister, 1936).

The time that we are concerned with, the Lower and Middle Miocene (about 16 to 26 million years ago), represented a rise in the sea level in California.

In summary, the Lower Miocene represents a time of transgression after the great regression of the Oligocene. Vaqueros sandstone, which probably may represent any stage of the Lower Miocene or all of it, was the initial deposit of the transgressing sea (Reed and Hollister, 1936).

Geology in Charmlee

The geology of the park consists mainly of two formations, the Vaqueros formation of the early Miocene, and the Topanga formation of the middle Miocene (Fig. 3. They are very similar in many ways. They both consist of near-shore marine sandstone and contain molluscan fossils that are common to the area, although those in the Vaqueros formation are slightly older. Further evidence of their marine origin exists in the interbeds of siltstone and mudstone, which are frequently found in marine environments where sediment grains are very fine.

The Topanga formation is characterized by the presence of pebble-cobble conglomerate bed, which is not present in the Vaqueros formation. This means that many of the sediments in the Topanga formation were deposited by rivers flowing into the ocean, whereas the sediments in the Vaqueros formation were not deposited by or near rivers. This feature is a clear indication of a change in the paleogeography of the environment around what is now Charmlee Park (Campbell, 1996).

In addition, the grain size in the Topanga sandstone tends to be slightly larger than that of the Vaqueros sandstone. This is seen in the differences in weathering patterns between the two formations. The Topanga sandstone weathers in an uneven mushroom shape, forming small cave-like structures called tafoni. They are formed because the large grains are not very closely packed, and there is more room for rainwater to seep in between the grains. The water, having reacted with carbon dioxide to form carbonic acid, dissolves the calcium carbonate cement holding the grains together, loosening them. Through capillary action, the water later moves to the surface, carrying with it the dissolved carbonates. The water evaporates and leaves the cement in the surface of the rock, forming a crust that doesn't weather as easily and causing an uneven weathering. Vaqueros sandstone, on the other hand, has finer grains and is, therefore, better indurated than Topanga sandstone, and it generally weathers more evenly, since this process doesn't occur as often (Ramírez-Herrera, personal communication, 2003).

A map was produced showing the boundaries of Charmlee Park superimposed on a digital orthoquad (DOQ), or georectified image of the area Fig. 4. On this map were shown the locations of several points of geological interest. Photographs and short explanations of some of these points are shown in Fig. 5.

Further developments in this project are pending. The map of geological points of interest will be printed as a high quality paper map along with a collection of photographs from all points shown, each with an explanation of the features shown. This map packet will be made available to the City of Malibu and the docents of Charmlee Park to assist them in explaining the geology of the park to visitors. A clickable interactive web map is also under development, in which site visitors can click on the points shown and be taken to the photographs and explanations, in a sort of virtual geology tour.

1. Campbell, R.H., et al, "Geologic Map of the Point Dume quadrangle, Los Angeles County, California", USGS, 1996
2. Dibblee Jr., Thomas W., and Helmut E. Ehrenspeck. 1990. "Geologic Map of the Point Mugu and Triunfo Pass Quadrangles, Ventura and Los Angeles Counties, California." Santa Barbara, CA: Dibblee Geological Foundation.
3. Harrison, Tom. 2001. "Santa Monica Mountains West Trail Map."
4. Ramírez-Herrera, María-Teresa, Ph. D. 2003. Personal communication (July).
5. Reed, Ralph D. 1926. Geology of California, American Association of Petroleum Geologists (reprinted 1951).
6. Reed, R. D. and J. S. Hollister. 1936. Structural Evolution of Southern California, American Association of Petroleum Geologists (reprinted 1951).

Acknowledgements We would like to thank Dr. Chrys Rodrigue, who was interested in Charmlee Park and created a project out of it, as well as facilitated the visits to Charmlee Park. Brian Sims and Dr. Chris Lee drove us to the park and helped us learn how to use the GPS units. The staff at the Geography computer lab, especially Aziz Bakkoury and Dr. Lee, helped us learn ArcView and were very willing to give of their knowledge, information, and time. Tom Tran of the SAS Computer Lab contributed much technical support. Dr. Teresa Ramírez helped immensely through her explanation of the geology of the area, her support in and out of the field, and her patience as we learned all this information and worked through the project. Dr. Beth Ambos, Crisanne Hazen, and the GDEP staff created this program and made this opportunity available to us. This project was funded by the National Science Foundation grant # GEO- 0119891. Thank you, everyone! Without you, this project would not be possible!!