BLACK HILLS: FUN AT FAIRBURN AND TEEPEE CANYON AGATE BEDS

 

It is that time of year when I present my yearly report on Fairburn Agate hunting in South Dakota!  Well, almost yearly since I missed the fall of 2020 due to a Covid scare.  This year I was rarin’ to go since I had three vaxs in my body. The first two were pretty easy while the booster gave me some minor “flu” symptoms.  However, I viewed that a small price to pay for some excellent protection from a very nasty virus.  In addition, we certainly were avid mask wearers when heading into town (Custer).  But, in fact, we rarely entered any establishment where people congregated---I like to think that my momma didn’t raise no fools.  We were camped at Custer State Park (Legion Lake) and I had plenty to do visiting with friends and relatives stopping by, driving the country roads looking at outcrops, having black coffee (prefer a French Press) while perched in my lawn chair enjoying the early morning sun, and enjoying a frosty IPA in the early evening coolness that was a harbinger of Fall.  In addition, the Harvest Full Moon made a beautiful appearance about the same time as the Fall Equinox.  And to top it off the planet Venus was in full bright bloom.  For an ole outdoor guy life was good.

LIFE IS GOOD SINCE I

DECIDED TO MAKE IT THAT WAY

I have noted in several other Blog Postings that Fairburn Agates from South Dakota are valued for their colorful fortification patterns with an abundance of reds (iron oxide), oranges (iron oxide) and blacks (manganese oxides).  The derivation of their name comes from the small community of Fairburn, located south along SD 79, ~25 miles south of Rapid City (north of Buffalo Gap described in the previous Post).  The “Fairburn beds” are also perhaps the easiest for collectors to locate.  Agate hunters should travel east from Fairburn along French Creek Road (good gravel road) for about 12 miles to a sign locating the original collecting area managed by the Buffalo Gap National Grasslands.  Although known to collectors for decades, these Fairburn beds still yield an occasional agate, and as many colorful specimens of jasper, quartz, and chalcedony as can be carried out in your collecting bag.  The beds were quite busy the day I visited, and the small primitive campground had seven sites filled.  A couple of the camp sites appeared to have been occupied for several days/weeks by hardcore agate hunters.

The agate beds seem to go on forever at the Fairburn site.

The red or reddish orange unit is the Interior Zone (zones of ancient soils) that developed on late Cretaceous to late Paleocene rock units although an upper red zone may be part of the Chamberlain Pass Formation, the lower stratigraphic unit of the Eocene White River Group.  Above the Chamberlain Pass Formation id the Chadron Formation that forms the "gray mound" topography.  The White River Group is the major unit forming the "Big Badlands."  The agate beds seem related the Chadron and Chamberlain Pass Formations.   

One could haul sack loads of semi polished quartz and microcrystalline quartz pebbles and cobbles from the beds.

This gentleman was tired of walking so pulled a chair and a book from his vehicle and was having a little read.

My knees simply do not allow for much hill climbing on the pebble and cobble size accumulation of quartz/microcrystalline quartz.  One a person starts skidding down hill there is little stopping!  At any rate, I sort of hobbled around and was able to collect a small agate right on the road.  I sort of laughed when I wondered how many hunters had walked and driven over this specimen.  Yep, life is good.

 

The small Fairburn Agate on a piece of polished jasper. Maximum width of the agate section ~1cm.

Since I was on my agate kick that day, it was time to grab my crack hammer and visit the source beds for the water-worn Fairburns found out on the plains surrounding the Black Hills. Teepee Canyon is located approximately18 miles west of Custer, South Dakota, about 2 miles west of Jewel Cave National Monument off U. S. 16.  As soon as travelers leave the Monument they should look to the west, up slope, to spot piles of broken rocks.  Sawmill Spring Road, FS 456, leads off to the west and about a mile further West Teepee Canyon Road takes off.  My best advice is to follow one of these roads/tracks and look for quarries where past prospectors have tried their luck.  The land is managed by the U.S. Forest Service and there are mining claims---I think.  It is best if rockhounds stop in the USFS office in Custer and discuss your plans with one of the friendly employees. 

Although hardcore agate hunters like to use pry bars and other large utensils to excavate layers of limestone and crack them open, older gentlemen like me prefer  to crack on the large “hunks” (basketball size or so) left behind by the previous diggers. There are literally thousands and thousands of “hunks” in major piles that are scattered over a large amount of real estate.  My suggestions: wear heavy boots, long pants, a long sleeve shirt, leather gloves, and eye protection.  The limestone is quite dense and the siliceous nodules very hard and chips fly when meeting a crack hammer.  Also, don’t try to trim out an agate in the field—take it home to work on the nodule.

No need to dig at Teepee Canyon.Just grab a hunk and crack!

The agates are encased in chert nodules housed within the lower Minnelusa Formation (Paleozoic: Pennsylvanian).  I suppose these nodules are the result of silica-rich meteoric waters circulating through the unit with resulting diagenesis producing the chert.  Why some nodules are agatized—I don’t have the slightest idea.  Just as I am uncertain how/why agates really form! What is clear, at least to me, is that the similarity of the Teepee Canyon agates encased in chert seem identical to the water transported Fairburns found on the plains.

Section of chert nodule from Teepee Canyon with nice display of agate.  Width of FOV ~3.1 cm. 

Small, interesting agate from Teepee Canyon (reverse of limestone matrix). Width FOV of lower photomicrograph 1.5 cm. 

Small, interesting agate from Teepee Canyon (obverse of limestone matrix). Width FOV of lower photomicrograph ~1.5 cm. 

However, my best Teepee Canyon agate collected this year came not from banging on a nodule but by paying $5 at the recent CSMS rock and mineral show.  Someone had evidently donated a sawed nodule with a gorgeous agate exposed and the club had it for sale on the silent auction table.  I put in a bid and kept a close watch to see if other bidders were interested.  None were and I scooped up a real bargain without a single blow of the hammer.  I suspect that not many people realized the source and significance of the slab.

The Teepee Canyon agate purchased from the Silent Auction table at the 2021 CSMS Show in October 2021.  The width (longest) of the paper is ~1 cm.

So, the agate hunting was “OK” this year, not spectacular but anytime you find an agate, big or small, is a good and successful day.  

My mission in life is not merely to survive, but to thrive; and, to do so with some passion, some compassion, some humor, and some style.  Maya Angelou

 

HAPPY NATIONAL FOSSIL DAY: OCTOBER 13

 

Having fun with fossil Musk Oxen (Bootherium bombifrons; formally Symbos cavifrons). Collected in shoreline gravels of Pleistocene Lake Bonneville. Nelson, M.E., and J.H. Madsen, Jr., 1987, A review of Lake Bonneville faunas (Late Pleistocene) of northern Utah in Cenozoic Geology of Western Utah--Sites for Precious Metal and Hydrocarbon Accumulations, Utah Geological Association Publication 16.