Geology Question

[Slots-R-Us]

I've traveled the length of the lake from Wahweap to Hite and find the change in the geology from one end to another quite fascinating. I've heard the story of the Lee's Ferry steam boat that was going to "mine" surface coal to provide energy for the Ferry station. There were surface level deposits of coal they found down river. Apparently, the coal was very low grade and they used it all up getting the steam boat back up to the crossing. My question relates to rock formations as you leave the Rincon moving down lake towards the Escalante arm. Many of the rocks turn very dark, almost black. Does this rock have coal in it or is it some other mineral causing the color?

Just got back from my second trip this year. It is definitely worth the ride to see Gregory Arch! Have waited in anticipation to see it. A bit sad that 50 mile canyon only goes up a short ways at this level. I think it is one of the most beautiful canyons on the lake. Can't have it both ways though! It is great there is always something new as water levels fluctuate. Continue to love Cathedral in the Desert, it is amazing how much sand was deposited in there and then how much of it has been washed out. Nature is constantly changing things.

 

[drewsxmi]

Geologists among us? There were some small coal mines in Crosby Canyon (west side of Warm Creek) among that grey gumbo mud, and some really big coal deposits in Smoky Hollow in the main Warm Creek drainage. The Rincon is an anticline (uplifted fold) and I believe the rocks / mud at the bottom are part of the Chinle formation. It's about the southern end of the Waterpocket Fold. On the north side of the channel just downriver from the Rincon is "Oil Seep Bar." I don't recall any really dark rocks. The Chinle formation is known for dinosaur tracks and petrified wood. Somebody in another thread a few months ago described how the rock formation tracks with the lake width. Soft rock like the Chinle formation means large bays like Good Hope Bay.

 

[scubatim]

Geologists among us? There were some small coal mines in Crosby Canyon (west side of Warm Creek) among that grey gumbo mud, and some really big coal deposits in Smoky Hollow in the main Warm Creek drainage. The Rincon is an anticline (uplifted fold) and I believe the rocks / mud at the bottom are part of the Chinle formation. It's about the southern end of the Waterpocket Fold. On the north side of the channel just downriver from the Rincon is "Oil Seep Bar." I don't recall any really dark rocks. The Chinle formation is known for dinosaur tracks and petrified wood. Somebody in another thread a few months ago described how the rock formation tracks with the lake width. Soft rock like the Chinle formation means large bays like Good Hope Bay.

The coal is in the Dakota sandstone. Geologic formations in the south are basically the same as up north - some thickness differences but still (in ascending order) Wingate ss; Kayenta ss/shale (dino tracks); Navajo ss; Carmel shale; Entrada ss; Morrison Fm (green shales, ss; Uranium); Dakota SS with coal seams.
The area north and northwest of Warm Spgs has numerous coal mines, probably abandoned in the Fifties. The Dakota caps the Kaparowits Plateu north and northeast of the area of Padre Bay. One "oil seep" is mapped but probably just water flowing in the coal seam from the north.
The Rincon is on the crest of an anticline (upwarp) and is an old "cut off meander" of the Colo River - prior to breaching the full thickness of the Carmel shales. The Chinle is below the Wingate.
The dark stains on the surface of the sandstones (particularly the Wingate) is "desert varnish" which is an oxidized manganese coating. Where there is more iron than manganese, the stain is more reddish (ie the red streaks on Tapestry Wall).

 

[drewsxmi]

A little more follow-up, it didn't occur to me that the dark color you described might be desert varnish on the harder sandstone cliffs.

In my experience around the Colorado Plateau coal seams are quite soft, and usually erode faster than the layers above and below them, so you rarely see an exposed coal seam, except in road cuts. The coal just erodes away too quickly, and the other rocks cover it. Coal does not make steep cliffs like the Navajo sandstone around Glen Canyon Dam.

If you drive through Price Canyon there are a few thin exposed coal seams in the road cuts near Castle Gate.

 

[Don S]

the dark streaks are from Iron oxidizing.