Tuesday, November 4, 2008
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.