On Sunday, 3/2/08, a number of collectors from the Houston Gem and Mineral Society met in College Station to spend the day collecting petrified wood and searching for new locations. These paired cities sit on the outcrop of the Eocene Yegua formation, which is known in Texas to have petrified wood. The environment in the Texas Eocene was sub-tropical, so many different species flourished here, none of which are found in the area today. The College Station/Bryan area is near the Brazos River, and the ancestral Brazos is known to have moved over a large area in the past, eroding the Yegua Formation and concentrating the petrified wood exposed by the erosion with sand and gravel in river bars. Collectors search for evidence of these bars because the amount of wood that can be examined and collected is much higher in these layers than in the rest of the formation as a whole.
We started off our morning on White Creek, which is accessible where it crosses a major roadway. White Creek is eroding a shale layer of the Yegua, and there is a large sand and gravel bar above the contact that also spills petrified wood into the stream. White Creek is a hard area to collect, since the wet Yegua shale is extremely slippery and there are several areas where the water gets quite deep and getting around is limited by fallen trees and brush. Downstream access is limited by closed roads for Texas A&M U. installations and the airport. Large pieces of petrified wood up to 125 lbs have been found beyond the fallen tree area, creating all sorts of problems in getting the specimens back out. The locality is most famous for one type of wood found there and nowhere else in the area. Soft, common opal silicified logs with chalcedony fillings in the central shrinkage cracks are found here, eroded into unusual shapes and showing the cross sections of the "centers" with the chalcedony. These limbs and centers of logs can be up to 6" across, but most are 2 - 3" across and 12 - 18" long.
One of our members went far down the creek and reported nothing new had eroded out since he had last been there, so we limited ourselves to the upper part of the creek. One of the interesting features of the Yegua shale is a regular joint set due to regional tectonic stresses. These joints are often filled with white to gray gypsum var. selenite crystals, which are occasionally worth collecting.

The rest of the morning was spent in the NW part of Bryan, driving to stream crossings, gravel pits and other potentially interesting areas that our Google and Mapquest maps had revealed, to see if we could locate any new collecting sites for wood. While the drive was interesting our stops were not productive, and we saw a lot of barbed wire across creeks guarding access to areas that might be productive.

We ended up before lunch at a tried and true locality, a hidden dry wash on land that is not yet developed, though there was a sign stating the intention of a local church to make the plot their home. This dry wash erodes a very thick bed of secondary deposition by ancient rivers, and the bed of the wash is full of large pieces stacked like cordwood in the mud and sand. Though people have been collecting here for a year and a half, there is still a lot of wood to be found. I actually found the biggest piece, 4" across and 30" long, lying under leaves next to a tree with only one end exposed. Between all of us we easily took 400 lbs of petrified wood chunks out of the stream bed and slopes in an hour of hard work. Most will go in our gardens, but some of the smaller pieces are good for cutting and tumbling and some have beautiful twists that make them attractive as specimens.

More tomorrow on how we spent the afternoon.

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