Question: Where did the River Rock at Lake Powell come from?

[Pegasus]

I've always wanted to bring a geologist familiar with the Lake Powell rock structure down to the lake with me, but haven't been able to make that happen (because I don't know of anyone with this knowledge - the offer is open for a free trip!). We explore the Lake year-round and have always been fascinated with the river rock that is spread throughout the lake (southern lake specifically) at elevations that were pre-Lake Powell.

How did this rock get here? What time period was this? What was going on at the time that this rock was deposited? There are several HUGE river rock mounds mid-lake, near Anasazi Canyon. And at many other places along the channel. Can any of you WW'ers educate us on where/how this rock got to where is it now?

The photo below is just to the south of APM between the marina and the public ramp, with an abundance of river rocks present.

 

[BartsPlace]

I'm no expert. But I too find this fascinating. Some of what you ask is described in the Kelsey book and others. Generally, the thought is that they have been moved to the canyon/lake during heavy runoff and flash floods. There are several slot canyons on the north end of the lake (west shoreline) that have blue granite rocks which have been washed down from the Henry Mountains that are several miles away.

I've always wanted to be able to turn back time (similar to the Google Earth feature) and watch what was happening at a given period or event. Your photo also seems to have many shells among the rocks. I'd love to have more of their history as well.

 

[Flipper]

I'm no geologist but I can tell you that those rocks were deposited from old river channels through eons of time. When the river changed, those rocks were left high and dry. There are large river gravel islands all over the lake. There are three large ones on the east side of the main channel just north of Castle butte in Good hope bay. There are 4 more at the horn, and a large one in 4 mile. When these are submerged, they make good walleye habitat. The river channel is constantly changing depositing silt and gravel from all of the drainages of the Green and Colorado rivers. I have found Yellow sandstone with brown veining on the bank behind the houseboats at Hall's that is Identical to some that I have bought from the rock shop in Grand Junction. These particular rocks are very unique and had to have come form the same location, yet now there are scattered over hundreds of miles. Look at all the weird rock formations all over at Powell, all that was created by the power of water and gravity, wind and freezing. Look at the Rincon, the river used to flow another three miles around it before it cut it self a shortcut. I was a coal miner for 25 years. I have seen dinosaur footprints in the roof were the black slate fell after the coal was mined out from under it. We were as much as 2000 feet under ground. I often wondered how that much rock got deposited over the old creeks and bogs that the footprints were left in?

 

[Havalina]

This is just a swag, but it took several hundreds of thousand of years for the colorado to wear its way down to make a canyon. I have never been down to the southern end of the lake. The northern end has quite a few of conglomerate rock structures. Maybe the binding of the conglomerate eroded faster leaving the larger stones.

I am pretty sure that there is some conglomerate erosion where good hope bay starts.

 

[Canyon Glen]

forgot where I heard the ancient desert was fairly flat for miles with an ocean on one side, meteors shrinking the water would send tsunamis rushing over the desert and then swirling back in to the ocean basin displacing rock along the way

another guess is the cobbles were formed in an ancient river long before the Colorado started carving it's way to the ocean

 

[Dave I.]

The truth be told, I am no Geologist but we see sooo many rock hounds here in Hanksville, these kind of conversations come up.

Here on my property, I was leveling a hill with my skidsteer and started to unearth river rock and river washed petrified wood. Yes here in dry land Hanksville. These tumbled rocks and wood are from the Triassic period of earth's timeline and during that period, Hanksville was at the bottom of a shallow inland sea. Since Powell is lower than Hanksville, naturally the river rock would migrate to lower elevations.

If anyone wants to stop by see the river washed petrified wood, feel free. Always love to meet other Worlders.

 

[shanewave]

Fascinating info from all of you...