Photos for Gateway, Colorado

More Photos for Gateway, Colorado

Here on the west side of Unaweep Canyon, and the west side of the Uncompahgre Plateau, you can see what got deposited along the side of the Uncompahgre during the Permian. These rocks are debris flow, mudflow, and stream deposits. The clasts in the debris flow deposits, as well as the finer matrix, make it possible to determine the source area for these sedimentary rocks. So, what is the source? And, more importantly, HOW can you determine where these sedimentary rocks were derived from?

Alluvial fan deposits on the west side of Unaweep Canyon

This outcrop is exposed along 4and 2/10 Road (yes, it IS an odd name for a road) in the town of Gateway. Here the rocks are still representative of the Gateway Fan, but these were deposited further away from the Uncompahgre, that is, more distally. This exposure contains evidence of fluvial and floodplain deposition. What sorts of features are used to identify rocks deposited by rivers? What features are common on floodplains?

This photo looks from the west toward the town of Gateway and the Gateway Fan. The light colored rocks in the bottom half of the slope are the fan deposits. Above the fan, the Triassic Chinle Formation is present, and is overlain by the Wingate Sandstone. Generally Permian rocks in this part of the world are overlain by the Triassic Moenkopi Formation, but here the Moenkopi is missing and the Chinle directly overlies the Permian rocks. There are several reasons why the Moenkopi might not be present, what are some of the possible reasons?

This photo is actually taken at Fisher Towers, located in Utah to the northeast of the town of Moab. These strata were probably deposited at about the same time as the Gateway Fan, and represent an extremely distal part of the fan or another fan altogether. The strata here are called the Cutler Formation, undifferentiated. We will see a lot of Cutler later on, and further to the west it gets differentiated into different formations. There is evidence of fluctuations in the strength of the flow of the streams that deposited the Cutler at this location. In this photo, a relatively coarse layer overlies a relatively fine layer of rock, and the two layers are separated by an erosional surface. What physical changes cause a stream to be able to carry larger material at one time than at another? Could climate control some of these physical parameters? How about tectonics?

Here at Fisher Towers there is a distinct alternation between light purple and dark purple beds. Most of the dark purple beds represent stream deposits. The light purple beds represent stream and eolian (wind-blown) deposits. The cyclic nature of the Cutler Formation deposits at Fisher Towers may reflect changes in climate. Why?

This photo shows the Gateway Fan as viewed from the south along the Dolores River. The fan consists of the light colored rocks in the lower one-quarter of the slope. Note that the fan dips to the left in the photo (to the west). This dip direction is oriented away from the Uncompahgre Uplift, and that is a bit of information that helps to identify the Gateway Fan as an ancient alluvial fan.