INTRODUCTIONI am very fortunate to live in the city of FOLSOM, California.It is located in Sacramento County and situated in thewesternmost foothills of the Sierra Nevada Mountains, onthe Southwest side of the American River in NorthernCalifornia.There is a lot of rich history in thegeology and landscape of the area.It sits 27 miles from Coloma, CA,where gold was originallydiscovered, and is about 85 milesfrom Lake Tahoe, Nevada.It’s most commonly known for itsgold rush history and prison.
FOLSOM HISTORYFolsom has rich Western expansion history, with the California GoldRush and arrival of the railroad. Gold was first discovered along thesouth bank of the American River in the area known as Negro Bar.The discovery led to huge gold mining operations, along with theneed for a rail service (“Celebrating”, n.d.). It’s named in honor after U.S. Army Captain, Joseph Folsom, who purchased the land in 1847 and established the town for supporting gold mining and dredging activity. The area is surrounded by rolling hills, and was the final destination of the Pony Express (from Missouri) when it was functional in the mid-1800s.
FOLSOM STATE RECREATION AREAThe Folsom Lake State Recreation Area (FSRA) is a massivereservoir that Was formed by the Folsom Dam, constructed in 1955 tocontrol the American River. It has over 11,500 surface acres, almost75 miles of shoreline, and was placed just below the convergence ofthe north and south forks ofThe American River.The dam and lake are bothpart of the “Folsom Project”,which provides flood control,drinking water, irrigation,And hydroelectricity to thearea (Crockett, n.d.).
FSRA GEOLOGYThe Folsom Lake State Recreation Area is located betweenthe central Sierra Nevada and the Central Valley geomorphicprovinces. The Sierra Nevada is characterized by a north-northwest trending mountain belt with a broad region offoothills along the western gradient. Located above theFolsom Dam, it occupies the lower sections of canyons ofthe North and South Forks of the American River, with apeninsula stretching between the two arms of the lake.Lake Natoma, located downstream from the dam occupies abroad river valley that is cut into sedimentary rocks, andends at another dam called the Nimbus Dam. It occupiesthe stretch between both dams.
FSRA GEOLOGYThree major geologic divisions occur in the area: A north-northwest belt of metamorphic rocks with included ultramafic rocks (dense, rich in iron and magnesium). Granitic plutons that intruded and destroyed some of the metamorphic belt. Low-lying deposits of volcanic ash, debris flow, and alluvial fan deposits that overlie the older rocks. These divisions have created a varied and interesting geology for the area (“Environmental Conditions”, 2003).
FSRA GEOLOGYThere are four primary rock divisions found inthe area: Ultramafic Methamorphics Granodioriteand Granitic Volcanic Mud Flows Each is linked with a particular part of tectonic history, and each has distinct mineral resources (“Environmental Conditions”, 2003).
FSRA GEOLOGY Ultramafic rocks - The ones found here represent the lowest part of the Earth’s crust, and have been lifted as much as 20 miles vertically by the faulting and regression of other pieces of crust – most likely when it was added to North America by accretion. Minerals associated with the rocks in the area include chromite, talc, asbestos, and nickel (“Environmental Conditions”, 2003). Metamorphics – are bands of metamorphosed sediments and igneous rocks that occur through most of the peninsula and southern area of the lake. They represent ancient chains of volcanic island arcs and the respective seafloor sediments over a long time period (Jurassic and Cretaceous). The terranes are separated by faults, and the age of these rocks go back over 160 million years. Minerals associated with the rocks in the area include copper, zinc, and gold (“Environmental Conditions”, 2003).
FSRA GEOLOGY Granodiorite/Granitic rocks – slightly different than granite, they have slightly more iron and magnesium producing materials, and less quartz than granite. The crystals range in size, and the rock is coarse with a grainy appearance. The granitic rocks actually form the core of the Sierra Nevada, cooled from rock melted during the subduction process. Volcanic Mud Flows – the west side of Lake Natoma (area below the Dam) volcanically collected sediments mixed with volcanic mudflows (Miocene – Pliocene aged). Above them is a sequence of gravel, sand, and slit derived from granitic and metamorphic sources by way of debris flow and stream deposits – called the “Laguna Formation” (Pilocene aged) (Clark, 1970).
FSRA WILDLIFERabbits, raccoons, skunks, possums, deer, grey foxes, geese, andcoyotes are regularly seen in the park and surrounding area. Thepark also houses California horned lizards and western pondturtles. Mountain lions, bobcats, and rattlesnakes also frequentthe area but are rarely seen (“Folsom Lake”, n.d.).
FSRA PLANTLIFE The area is abundant with oak trees (live & blue) and foothill pine trees. Wildflowers bloom all during the spring and summer (“Folsom Lake”, n.d.).
BIKE AND PEOPLE TRAILSFSRA also maintains 34 miles of bike and pedestrian trailswhich follow various creeks, dredger trails, and riverbankforests. Many of the trails intersect the city’s open spaceareas, greenbelts, and wetland areas.The “American River Trail” isconsidered to be one of the finest biketrails in the state of California. It loopsunder the Folsom Lake crossing andcontinues alongside the westshoreline of the American River.There are incredible views of the riverand surrounding habitat such as theoak trees, granite rocks, nativevegetation and wildlife (“Discover”, n.d.).
MY FIELD RESEARCHDuring my exploration around FSRA, I located granodiorite, granitic, andmetamorphic rocks. I also located California Pine and Oak trees, andspotted geese swimming along the riverbank. ALL of the following pictures were taken by me with my own camera! View from above Folsom Lake View from Folsom Lake (ground level)
MY FIELD RESEARCH Trees behind me (including Oak) Metamorphic rocks right in front of me. A better view. I HAD to touch it!
MY FIELD RESEARCH Looking east at the rolling foothills. Alongside Folsom-Dam Road. This granite is HUGE! Almost my size. Yikes!
MY FIELD RESEARCH Looks like Granodiorite. The Folsom Dam – close as I could get. Base of the dam. Lots of granite beds.
MY FIELD RESEARCH Downstream from dam. Prison on left. There’s granite everywhere in Folsom! California Pine Tree. California Pine along the American River.
MY FIELD RESEARCH The American River. Upstream (towards Folsom Dam). All along the riverbank. Underneath an Oak Tree.
MY FIELD RESEARCHFurthest downstream at Nimbus Dam. Facing upstream, Geese came right up to me! eastern foothills in back. All along the riverbank. Nimbus Dam.
SELECT LIST OF REFERENESCity of Folsom: Celebrating Folsom’s Rich History (n.d.). Retrieved from: www.folsom.ca.us/about/history.asp.Discover Folsom.com: Recreation, Folsom Trails (n.d.). Retrieved from: www.discoverfolsom.com/recreation/folsom-trails/.Geotechnical Consultants, Inc. (2003). Environmental Conditions Geology: Folsom Lake State Recreation Area. Retrieved from: www.parks.ca.gov/pages/files/Geology.pdf.Golden Gate: Granitic and Grandiorite FAQ (n.d.). Retrieved from: www.nps.gov/goga/forteachers/granite- and-granodiorite-faq.htm.Parks Guide: Folsom Lake State Recreation Area (n.d). Retrieved from: www.parksguide.com/folsom- lake-state-recreation-area/.Todd Crockett (n.d.). Folsom Lake Information Guide: Folsom Lake-Good Fishing for Sacramento Residents. Retrieved from: http://www.jimporter.org/lakes/folsum/.W.B. Clark, (1970). Gold Districts of California: California Department of Conservation, Division of Mines and Geology, Bulletin 193. Retrieved from: http://museumca.org/goldrush/dist-folsom.html.Wikipedia: Folsom, California (n.d.). Retrieved from: www.en.wikipedia.org/wiki/Folsom,_California.