Government Canyon State Natural Area and the Witte Museum, have a coordinated effort with researchers from the University of Texas at San Antonio, Trinity University, and San Antonio College to analyze, document, and preserve the dinosaur tracks found in Government Canyon State Natural Area. As these professionals study the evidence of ancient life, they are incorporating time-proven techniques as well as Global Positioning System (GPS), Light Detection and Ranging (LIDAR) imaging, and 3D photogrammetry technologies. The collected data will provide a better understanding of track preservation and paleoecology of the dinosaur fauna present in Bexar County, Texas during the Early Cretaceous.
Casts of some of the tracks are on exhibit to in the Witte Museum's Naylor Family Dinosaur Gallery. You will get to see very well preserved tracks made by sauropods and theropods. Sauropods had 4 legs, rounded feet, and ate plants, while theropods had 2 legs, 3 toes, and ate meat such as the Tyrannosaurus rex.
Geological Discussion:
Scientists estimate that the dinosaur tracks at Government Canyon State Natural Area were formed approximately 110 million years ago during the Cretaceous Period. There are nearly 300 tracks including some partial prints. The tracks are known as "trace fossils" to geologists and provide important clues about how dinosaurs interacted with their environment. These imprints give scientists a snapshot record of activity while the organism was alive (as opposed to other types of fossils that are formed after the dinosaur died). The tracks give vital data about how the dinosaurs walked, their stride, and if their front limbs made contact with the ground.
How did the tracks get here? Begin by understanding that, 110 million years ago, this area of San Antonio was actually a beach! Where you are standing was the shoreline of the Gulf of Mexico. The Early Cretaceous Glen Rose Formation (115 to 108 million years ago) represents a period of large-scale sea-level rise in which the ancestral Gulf of Mexico was beginning a long, slow, encroachment over Texas. Occasionally sea-level would fall and expose the carbonate platform that had formed at the bottom of the shallow sea. This new shoreline would then become an open corridor that would allow animals to move freely from one area to the next. (In other words, the dinosaurs were walking along a mucky-yucky shoreline. The composition of the ground had a lot of limey, clay-like material and was not sandy like we normally think of when we think of a beach.) The track makers (in this case, dinosaurs) would walk along the moist but firm, fine-grained, limey mud of the shoreline and leave their tracks. The footprints would remain exposed for a short while, allowing them to become drier and harder (and thus able to resist damage during subsequent burial). When sea level began to rise again, the prints were gently buried with additional sediment. While buried for millions of years, the original sediment lithified (turned into limestone). Finally, the tracks became re-exposed by erosion or other forces. In other words, once the tracks were made in the yucky-mucky limey shoreline, the shoreline remained exposed and was able to dry out for a long time. This drying out causes the soil to harden into rock (lithifies) and then, when the shoreline changes again and begins to cover up the exposed tracks, they are hardened and able to resist erosional processes.
Please do your part to PROTECT the Dinosaur Tracks!
To get to the tracks: Follow the posted coordinates to just north of the Joe Johnston Route (JJR) trail signpost #19, about 2.5 miles from the JJR trailhead. This is an approximate 5 mile round trip hike and you should plan at least 2 - 4 hours to complete it. Be prepared and bring plenty of water with you.
To claim this Earth Cache, email or message (Do NOT post in your log) the Cache Owner with the answers to the following:
1. From the interpretive panel at the posted coordinates - What are the dimensions of the imprint in the rock left by the largest Sauroposeidon at Government Canyon State Natural Area?
2. From just looking at the rock formation (Do not attempt to measure in any way), approximately how tall is the sedimentary rock cliff near the posted coordinates? (Just an approximation, please.)