NOTE: I was going through some past caches to meet a challenge requirement and I saw this cache, American River At Nimbus - GC1674E by 2Dee2Dee, had been archived. I hate to see a good EarthCache go down, but especially one in this area, an easy grab with some good information, a wonderful view, a good little walk, all that stuff. So I figured I would try and get this one reposted. I remember hiking up to this location and looking out over the river, it was great. Reworked some of the questions and relooked up information originally provided and updated that. The premise of this cache is the same, but has been updated to be different enough from the original to be worth another visit.
NOW THE CACHE:
With seasonal Salmon and Steelhead runs, the river and lakes formed by the flood control dams on the American River provide a shared recreation area bounded by extensive nature areas and multi-use trails. It is also home to many migratory birds and ducks.
American River at Numbus
Free Parking Coordinates N 38 38.006, W 121 13.432
TO LOG this cache stand as near as possible to 38 38.119, -121 13.469 to observe acceptable answers to the following questions about the area. Some research may be required. Send your answers with the Geocaching Messenger, THEN, go ahead and post your found log, no need to wait for my reply, I will reach out if there is an issue with the information you provide. At the observation point you should see a plaque, this is the view point for making observations on the cache here.
QUESTIONS:
- First, let me know how many and who is in your group, only need to send answers once as a group, so write their names and just answer the following and send the response once.
- Describe the Geologic differences between the North and South banks of the river.
- Looking at the North bank you will see a “cliff-face” of rocks. How many layers can you count in this face and what colors can you observe from you observation point?
- Water is a very powerful erosive force. Can you see evidence of water erosion from your vantage point? If so, please describe it. Also, how do you think the construction of the dam has affected ongoing erosion along this part of the American River?
- Look towards the dam to the East. How many operable sections are there at the time of your visit?
- OPTIONAL: Post a picture of yourself or your team, your GPS, or something this your Geocaching name on it from the observation point.
The American River Division of the Central Valley Project provides water for municipal and industrial use, some irrigation, and hydroelectric power and recreation. Flood control is provided through a system of dams, canals and power plants. The division consists of the Folsom and Sly Park Units, both authorized in 1949, and the Auburn-Folsom South Unit, authorized in 1965. The Folsom Unit is all on the American River and consists of: Folsom Dam, Lake and Powerplant; Nimbus Dam and Powerplant; Lake Natoma. All features of the Folsom and Sly Park Units are complete and in operation.
Nimbus Dam is a base load hydroelectric dam on the American River near Folsom, California. Approximately 8,700 acre-feet of water is retained by the dam. It is responsible for the impoundment of water from the American River to create the Lake Natoma reservoir. The dam stands 87 feet and spans 1,093 feet. Nimbus Dam consists of 18 radial gates, each with their own gate bays. These 18 gates today are the ones that were completed in 1955 along with the rest of the dam. Of the eighteen gates, four of them have had their coating system replaced. This protects the gates from a faster rate of corrosion. The other fourteen gates have the original coating.
The Nimbus Power Plant, constructed and operated by Reclamation, is located on the right abutment of Nimbus Dam, on the north side of the river. It consists of two generators. Each generator produces enough electrical power to power over 200,000 100-watt light bulbs, about 15,500 kilowatts of electrical power.
Nimbus Fish Hatchery is located in eastern Sacramento County, Nimbus Hatchery raises Chinook salmon and steelhead for release to the American River. Construction of Folsom and Nimbus Dams blocked access to natural spawning grounds of salmon and steelhead trout. To compensate for the loss of these spawning areas, Reclamation constructed a fish hatchery about a quarter of a mile downstream from Nimbus Dam. The hatchery is on the left bank of the river, about 0.3 mile below the dam. It is operated by the State of California with Reclamation funds. Work began on April 20, 1955 and was finished and accepted on October 17, 1955. About 4 million Chinook salmon and 430,000 steelhead released each year.
GEOLOGY: American River Bluffs. The Sacramento Valley is a structural trough occupying approximately the northern third of the Great Valley Geomorphic Province. This area is near the edge of a structural trough associated with the bedrock formation of the Sierra Nevada province. The trough is filled with marine, lacustrine and alluvial deposits. The American River at Nimbus is composed of variable topography. Along the north side, the higher elevations consist of the resistant material (bedrock) that composes the bluffs and slopes along the American River, while on the south side the lower relief is the result of a combination of low topographic, erodible material located within the floodplain of the American River, and of areas of man-made embankment fills above natural grade. The site is generally underlain by thin veneer of colluvium derived from the poorly to semi-consolidated sediments of the Turlock Lake Formation, over semi-consolidated sediments of the Laguna Formation. Quaternary and Tertiary-age alluvial deposits are composed of medium dense to dense silts, sands and gravels.
The Mehrten Formation is a geologic formation in California. It preserves fossils dating back to the Neogene period. The Mehrten Formation is overlaid by the Laguna and Turlock Formations. The Mehrten Formation is exposed in rock cut on the north side of the American River channel and is composed of moderately indurate andesitic conglomerates, sandstone and breccia.