Mosaic Canyon is a canyon in the northwestern mountain face of the valley which is named after a stream-derived breccia sediment with angular blocks of dolomite in a pebbly matrix. The entrance to Mosaic Canyon appears deceptively ordinary, but just a 1⁄4 mile (400 m) walk up, the canyon narrows dramatically to a deep slot cut into the face of Tucki Mountain. Smooth, polished marble walls enclose the trail as it follows the canyon's sinuous curves. The canyon follows faults that formed when the rocky crust of the Death Valley region began stretching just a few million years ago. Running water scoured away at the fault-weakened rock, gradually carving out Mosaic Canyon.
Periodic flash floods carry rocky debris (sediment) eroded from Mosaic Canyon and the surrounding hillsides toward the valley below. At the canyon mouth, the water spreads out and deposits its sediment load, gradually building up a large wedge-shaped alluvial fan that extends down toward Stovepipe Wells. This canyon was formed through a process of cut and fill which included periodic erosive floods followed by long periods of deposition and uplift. But due to the uplift, when the next flood occurred, it would deeply cut the streambed which forms stairstep-shaped banks.
Mosaic Canyon's polished marble walls are carved from Noonday Dolomite and other Precambrian carbonate rocks. These rock formations began as limestone deposited during Late Precambrian (about 850-700 million years ago) when the area was covered by a warm sea. Later addition of magnesium changed the limestone, a rock made of calcium carbonate, to dolomite, a calcium-magnesium carbonate. The dolomite was later deeply buried by younger sediment. Far below the surface, high pressure and temperature changed the dolomite into the metamorphic rock, marble. The Noonday Dolomite has since been tilted from uplift.
Pure white marble is the result of metamorphism of a very pure (silicate-poor) limestone or dolomite protolith. The characteristic swirls and veins of many colored marble varieties are usually due to various mineral impurities such as clay, silt, sand, iron oxides, or chert which were originally present as grains or layers in the limestone.
Mosaic Canyon was named for a rock formation known as the Mosaic Breccia. Breccia (Italian for gravel) is a term most often used for sedimentary rocks that are composed of large angular fragments (over two millimeters in diameter). The spaces between the large angular fragments are filled with a matrix of smaller particles and a mineral cement that binds the rock together. Some breccias, like the ones in Mosaic Canyon, form from debris flow deposits. The angular particle shape reveals that they have not been transported very far (transport wears the sharp points and edges of angular particles into rounded shapes). After deposition, the fragments are bound together by a mineral cement or by a matrix of smaller particles that fills the spaces between the fragments.
The parking lot is 2.3 miles in on an unpaved, gravel road, which is generally driveable in a regular car (I did it in a minivan!). The first mile or so of the hike is easy and passes through amazing scenery - make sure to check out both the breccia, which looks like rocks and gravel in cement, and the marble, which has smooth colorful streaks. After that, there is some more difficult terrain and rock scrambling. It is NOT NECESSARY to go past the easy part to do this Earthcache - but I highly recommend going as far in as possible!
The posted coordinates will bring you the beginning of the trail. To log this Earthcache, please send me a message with answers to the following questions:
1. The text "GC Death Valley Mosaic Canyon - Breccia and Marble" on the first line
2. How many people there are in your group (including non-geocachers) and their geocaching names
3. Examine some streaky marble. What colors do you see?
4. Examine some breccia. Estimate the size of the largest embedded rocks you see in the breccia. Are they smooth and rounded, or sharp and angular? What does this say about about the distance these rocks traveled before they became embedded in the breccia?
5. Please post a photo of yourself or a personal item in front of either some marble or some breccia. This photo is a requirement to prove that you were at the site! Logs without a photo will be deleted!
References:
https://en.wikipedia.org/wiki/Places_of_interest_in_the_Death_Valley_area#Mosaic_Canyon
https://en.wikipedia.org/wiki/Marble
https://www.nps.gov/deva/planyourvisit/mosaic-canyon.htm
https://geology.com/rocks/breccia.shtml