Mosaic Canyon Geology

BackRoadsWest presents:

Mosaic Canyon: Geology Lesson

There are many excellent examples of "geology in action" in Death Valley and Mosaic Canyon is one of them. Death Valley is renowned worldwide by geologists as being one of the best places in the United States to study recent geological events (recent in geological time, that is) and Mosaic Canyon has several examples. As you take your hike up the canyon, you will get a chance to see this "new" geology. We hope that this short, simplified "geology lesson" will enhance your hike up this spectacular canyon by giving you a better understanding of how the powerful forces of Mother Nature created it. To learn more about the geology of Death Valley as a whole, see the Geology chapter.

As with most geologic processes, those happening in Mosaic Canyon are complex. The mosaic walls of the canyon, for which it was named, are made of breccia [glossary]. Read more about this process below in The Making of Breccia section. Other parts of the canyon walls are made up of sedimentary [glossary] layers. These layers have been created by the erosion of the mountains above. The picture at left was taken near the mouth of Mosaic Canyon, on the left (east) side, and is a perfect example of sedimentary layering.

Another type of rock that you'll see all along the canyon is the beautiful marble that was formed billions of years ago. The main formation [glossary] found in Mosaic Canyon is called the Noonday Dolomite. This pale, tan-colored bedrock was formed about 700 billion years ago when this area was covered by the Pacific Ocean. Later, it was buried deep underneath other formations and was subjected to extreme heat and pressure where some of it metamorphosed into the wonderful marble you see today.

In more recent times (geologically speaking), Tucki Mountain was uplifted and the east side of what is now Mosaic Canyon was pushed up along a large fault [glossary] line. This uplifting of the east side of the fault exposed the many formations you see today, including the Noonday Dolomite, and is the reason why Mosaic Canyon formed here. As the east side of the fault rose, erosion began to carve the canyon as it was now the easiest way for water to run downhill.

A Young Mountain
As you approach Mosaic Canyon on the dirt road from Stovepipe Wells, look up at the rugged Tucki Mountain in front of you and notice the sharp edges on the face of the mountain. These edges are an indication that a mountain is "young".

Young mountains tend to have these sharp edges because they have not been exposed to the erosion [glossary] process for as long as the more rounded, typically older, mountains. And, because there is so little rainfall in Death Valley, it takes that much longer for the mountains here to get "rounded".

Mudflows
When rain does fall here, it typically happens in the form of a flash flood [glossary]. Unlike other types of mountains where erosion is constant from streams and rivers that run year-round, the waters of a flash flood are high-volume and fast-moving and they pick up a lot of dirt and debris along the way. These rushing torrents of water become so thick with dirt and debris that they change into a mudflow.

Every mudflow event is unique in its own way. The downpour from a thunderstorm is usually very localized and large volumes of water can fall in a relatively small area. The unique combination of dirt, rocks and other debris from this small area gets picked up by the fast-moving flood waters and is moved downstream in the form of a mudflow. As the mudflow looses its momentum and eventually stops, the water evaporates and the debris settles becoming a new layer of sediment in the canyon.

The thickness of the layer, how far it makes it downstream and what kind of material it's made of depends on the density of the material in the mudflow and the volume of water dropped by the thunderstorm. A combination of light-weight material and a high volume of water will carry the debris further downstream and probably make a thinner sedimentary layer. Heavier material or less water in the mixture can mean that the flow will leave a thicker layer and/or not travel very far downstream.

This mudflow scenario is repeated over and over, over centuries of time, and has created the variety of colors and textures of the many layers you see in Mosaic Canyon today.

The Making of Breccia
The Noonday Dolomite formation is made mostly of dolomite (made up of carbonates) and limestone. These carbonates in the dolomite add to the "cementing" process that goes on when there is a mudflow. As the liquid mudflows race down the mountainsides, they pick up rocks of all different sizes and colors. Once in the canyon, the mudflows pick up the carbonates from the canyon floor and mixes it with the rocks. The carbonates here act just like the carbonates found in commercial cement products and they quickly solidify the suspended rocks trapped in the mudflow.

This process, with just the right combination of materials and conditions, is what creates breccia [glossary]. Although there are many canyons in Death Valley where you can find examples of breccia, we think that Mosaic Canyon has some of the prettiest examples in the entire Park (see picture at right).

Mosaic Canyon also has an abundant amount of breccia examples. It is likely that breccia is so common here, as opposed to the neighboring Grotto Canyon, because there is a higher concentration of the cementing dolomite in this canyon.

Once a breccia layer is laid down, subsequent flashfloods and/or mudflows etch grooves into them as seen in the picture at left. These subsequent flash floods/mudflows are also responsible for the glass-like, polished finish of the canyon walls. The canyon floor is constantly being raised and lowered by a process called "scour-and-fill". Major mudflow events "fill" the canyon with debris and then erode, or "scour", it away with smaller events.

When hiking through the canyon, be sure to take note of the different breccia layers. Some layers have only a certain size of rocks while others have assorted sizes. Some have pieces of the tan dolomite in it and others have grey and black stones. Try to trace the different layers as you hike and see how far you can follow that mudflow event.

If this very simplified explanation of some of the geology in Mosaic Canyon has peaked your interest and you want to learn more, we recommend reading Geology Underfoot [references].

Last updated March 03, 2007.