September 24, 2006: Grays Quarry, Wyoming

One of many trip reports by Alan Silverstein.
Last update: March 6, 2008

From:  Alan Silverstein <ajs@frii.com>
Date:  27 Sep 2006 12:51:09 -0600
Subject:  Re:  [Rockhounds] Fall Fieldtrip Reports
To:  rockhounds@lists.drizzle.com

"...how about the rest of you... any other Fall fieldtrip stories out there?"

OK, since you asked... A few days ago on Sunday, I got a chance to visit Grays Quarry in Wyoming for the fourth time. This is a large limestone quarry on private property (the Grays are local ranchers) about 7 miles north of Glendo, in east-central Wyoming.

The quarry is cut into the southwest side of a hill on the west bank of the North Platte River. The hill is perhaps 200' high, and the quarry highwall is 100-150' high at points (although terraced). The limestone is heavily altered by silicification, and it features a mind-numbing variety of colorful druzy quartz coated vugs, agates, and jaspers.

(Incidentally, much of this same type of material can be found at many local highway outcrops or around Glendo Reservoir.)

From Fort Collins, Colorado, the drive is about 155 miles and 2+ hours one way. I'd hoped to head up Saturday morning with a kayak, camp on the north bay of Glendo Reservoir, and spend the afternoon collecting solid, pretty vein agates (up to 3" or so thick) on the shorelines, which is legal with prior notice to the state park.

Unfortunately we had a couple of pre-winter cold fronts arrive Wed-Fri, and the weather Saturday was cold and wet. Worse, the lake had dropped 40' since I was last there in June, and calling ahead, I learned there was no longer a north bay! I gave up and just did a day trip to the quarry. Sunday morning I could see that the north bay was now mile-wide mud flats with a trickle of river running through it, and cows munching on vegetation on the drier parts.

However, the Sunday weather was excellent, with fog remnants milling about the Platte valley as we arrived about 10:15 in Glendo and about 10:45 at the quarry. There were 6 vehicles and about 15 people in our small group, following the lead of the president of the Cheyenne club. The quarry floor was wet and muddy in spots! It apparently had rained overnight.

Some of us stayed until 6 pm (local sunset 7 pm) digging, busting up boulders, and/or surface collecting. It was sunny, cool to warm, and breezy to windy at times, which is fair weather in Wyoming!

Every time to the quarry the terrain is different as they blast and haul rubble to the crushers for roadbuilding. This time I didn't luck into any great vugs or veins, unlike the previous three trips, but still brought home about eight 3-gal buckets of material to sort, ranging from display pieces to tumbling material.

I did try digging one hole into shattered bedrock, and it was easy to take apart as usual, but this particular location yielded only white to yellow mini-botryoidal coatings, no blue/purple druzy (the real prize) and/or calcite crystals (dogtooths, or masses up to inches across). In another spot I could only find rubble, no bedrock. I spent a lot of the time surface-collecting over the top of the hill with friends.