Wednesday, November 19, 2008

Stratigraphy of Dead Horse Point

Stratigraphy is simply the record of strata layers in rock. Chronologically they follow what's called the law of superposition, which establishes that the oldest rocks are on bottom and the youngest rocks are on top. Pretty simple principle right? Well out at Dead Horse Point, which is right in the heart of canyon country, there's a far reaching, visible geologic, layered record of the history of the earth. Strata layers help geologists determine many components of geologic history like: environment of deposition, fossil record, and the sequence of events throughout the history of the world. To see the stratigraphical history of Dead Horse Point go to:

Colorado Plateau

The Colorado Plateau is located in the three states of Arizona, New Mexico, and Utah, with the central point lying just slightly west of the four corners area. The modern topography of this region contains, arguably, the world's most beautiful canyon country, arches, and desert landscapes known to man. Just to rattle off a few from an impressive list: Arches, Canyonlands, Grand Canyon, Bryce Canyon, Zions, and Capital Reef National Parks. Also found within this region are the laccoliths (Abajo, Henry, and La Sal mountains) of South Eastern Utah, Lake Powell National Recreation Area, and Escalante Grand Staircase and Natural Bridges National Monuments.
The Colorado Plateau has maintained a relative stability over the past 600 million years, this is unlike all the areas that are found along it's borders (Rocky Mountains, Wasatch Mountain Range, Uintah Mountains, Basin and Range Province). The Grand Canyon is one of the wonders of the world and is especially useful to geologists for it's stratigraphical rock record, dating all the way back to the Precambrian with 2 billion year old rocks! The Colorado Plateau region has been one of continual change throughout geologic time. In the Paleozoic era it was periodically inundated by ocean water from the east, thus forming thick layers of siltstone, limestone, sandstone, and shale from shallow marine water deposits. About 250 million years ago this region was greatly affected by mountain-building events (called orogenies) that caused widespread crustal uplift and formed new mountains obviously. The area then became a drainage plaine for the mountains that were to the west of the Colorado Plateau Area. These streams and lakes, made from the drainage of the western mountains, formed the Chinle, Moenave, and the Kayenta formations of the Mesozoic. Skipping much of the history we arrive at a more recent era of the Cenozoic where more uplift occurred, resulting in an increased gradient level. The streams of the region then started cutting down through the rock and formed much of the canyon country we now know today. Mass wasting and erosion of the cliffs produced spectacular buttes, mesas, and plateaus. The geologic history is rich and extensive, if you're interested in a more complete report of this area see and even though Renee doesn't like it, there's a lot of good information at The Colorado Plateau is home of some of the best, if the not THE best wild desert country in the world, take every advantage you can to go and see it.

Wednesday, November 12, 2008


(and really cool dudes)

Let's talk about laccoliths. First off, what is a laccolith? Where can I find a visible example of one? In response to the first question, according to a laccolith is an, "igneous intrusion (or concordant pluton) that has been injected between two layers of sedimentary rock. The pressure of the magma is high enough that the overlying strata are forced upward, giving the laccolith a dome or mushroom-like form with a generally planar base." As you can see behind the really cool dudes in this picture there lies a mushroom-like looking mountain, here, in is this case, it is the Blue Mountains, or the Abajo Mountains, in Southeastern Utah (the answer to the second question). As the definition states, a laccolith is an igneous intrusion, thus forming underneath the crust. Magma then pushes the laccolith upward along with the overlying sediment. Over a long period of time the sediment above the laccolith is then weathered away and the harder, igneous rock of the laccolith is left behind, finally exposed.
For another, simple picture of a laccolith see

Tuesday, November 11, 2008

How and Where Uranium is Concentrated

Do you remember when everyone was looking for uranium in Southern Utah? (If you don't check out this site it explains it.
Have you ever noticed that uranium mines are all in the same layer of rock? There is actually a scientific reason for that. Uranium is secondary to the rock, this means it was added after the rock was formed. What happens is water is heated up by magma and moves through permeable rocks carrying metals such as uranium. Uranium is soluble (able to be dissolved by water) when water is oxidized (has oxygen in it.) When that oxidized water with Uranium runs into rock with carbonized wood the uranium is dropped because the carbonized wood causes the water to reduce (lose the oxygen).  Notice that the mines  are all along one layer of rock because  the layer was full of carbonized wood. The layers of rock that have this are the Chinle and Morrison formations. In the picture above that  greenish color is the Chinle formation that has the uranium mines.

Tuesday, November 4, 2008


When we saw the top part of this layer we stopped at "The Neck," on the North East end of Canyon Lands National Park we were actually standing on the Glen Canyon Group which is the upper layers of the Triassic. We were standing in the Navajo Sandstone which looks like great rolling sand dunes, because they are petrified sand dunes. From the neck, if you look east, you can see down into a big canyon and see alot of different layers. The first we see is the Navajo Sandstone which is a white cross-bedded layer, underneath that is the Kayenta Formation. According to the Canyon Lands Pamphlet the rangers gave us in the beginning of the park, the Kayenta is formed from meandering rivers, and there are deposits of lime stones and shales in these layers. The Wingate Formation is right underneath and it is evidence of another really dry time, created by rolling sandstones and this layer too will have the cross-bedding we see in the Navajo. These three layers keep the cliffs pretty sheer and straight due to composition although with the Kayenta it is a bit 'stair step' look to it because of it's lesser Resistance to weathering. As we drop down we come to the lower parts of the Triassic Era and the cliffs turn into steep to shallow slopes usually covered mostly with eroded rock and sediment from the higher layers, but here we see the Chinle formation and the Moenkopi. they are layers of shale, clay, sandstone. They are formed under water and swamps. In the Chinle we find a lot of petrified wood. In that layer as well we find a lot of Uranium.
Here we get to the Permian Era about 250 million years ago. It is best seen as you look around the canyon and see where the shallow slope immediately drops off into anther canyon. There is a white layer of rock that runs around the rim and it is made of sandstone. Sandstone is less resistant, so it creates these crevasses. That layer is the top of the Cutler Group called the White Rim Sandstone.

Green River Overlook

Coming south east on I-70 through the town of Green River(where the Arby's has a great bathroom according to Renee:) Exit mile 181 at elevation 4782. Walking out to a pavilion looking south the first outcrops we see are the North end of Arches National Park. Also the first visible evidence of the Salt Valley Graben( graben being a German word for Ditch). We have learned already that grabens and Anticlines form in many ways. This one forming from salts deep below the earth's surface moving upward and creating a dome. Cracks at the surface allow water to creep down and dissolve the salt creating a cavern of open unsupported space beneath the ground. The earth collapses and leaves these fins above ground that we can see from this point.


The Jurassic layer is one of the higher layers we see in the Arches National Park and Canyon lands. The Slickrock Member in the Entrada Sandstone of the Jurassic is where we find the Delicate Arch of the A.N.P The bottom most layer of the Entrada is a layer consisting of silty sandstones called the Dewey Bridge formation. It is easily recognized because of it's pattern of erosion and it's deep red color. It looks like bricks and does not weather flat like a lot of the sandstone but more in a cobble stone look. On top of that sits the Slickrock member who's composition is sandstone, making it weather in sheer straight cliffs. Leaving smooth straight cliffs called "arch formers" that are red in color and have cross-bedding in them. The relationship between these two layers is where the formation of arches begins. The top most layer is called the Moab Tongue. This layer can be seen at the very top of the Delicate Arch, it is a white cross-bedded sandstone.