Ancient Riverbed EarthCache

This Earthcache is located along the bike trail at Negro Bar in the Folsom Lake SRA. At the posted coordinates you will find 2 information plaques relating to the Cliffs above this stretch of trail. All the logging requirements can be answerd from the posted coordinates and there is no need to leave the paved Bike trail.

In geography and geology, a cliff is a vertical, or near vertical, rock exposure. Cliffs are formed as erosion landforms due to the processes of erosion and weathering that produce them. Cliffs are common on coasts, in mountainous areas, escarpments and along rivers. Cliffs are usually formed by rock that is resistant to erosion and weathering  Sedimentary rocks most likely to form cliffs include sandstone, limestone, chalk, and dolomite. Igneous rocks such as granite and basatt also often form cliffs.

An escarpment (or scarp) is a type of cliff, formed by the movement of a geologic fault, or a landslide.

Most cliffs have some form of scree slope at their base. In arid areas or under high cliffs, these are generally exposed jumbles of fallen rock. In areas of higher moisture, a soil slope may obscure the talus. Many cliffs also feature tributary waterfalls or rock shelters. Sometimes a cliff peters out at the end of a ridge, with tea tables or other types of rock columns remaining. Coastal erosion may lead to the formation of sea cliffs along a receding coastline.

The cliffs located here were exposed when much of the hillside was washed away hydraulic mining. These exposed cliffs reveal the story of the Ancient Riverbed.

These layers were laid down over a period of more than 10 million years. Look at the exposed layers, you will see layers of river cobble, sandstone and clay.

The dark overhangs are from the volcanic mudflows. The mudflows are harder than the lighter colored, softer sandstone deposits which erode more easily. You can see how the sandstone has eroded away leaving the harder material in place.