Dinosaur Ridge near Morrison, Colorado

Dinosaur Ridge is a Mesozoic “hogback” (a resistant ridge) in Colorado, near the town of Morrison, west of Denver. On the west side are Upper Jurassic mudstones known as the Morrison formation.  Dinosaur bones and some footprints are found in the Morrison. On the east side are younger Cretaceous sandstones, the Dakota formation.  Most of the dinosaur footprints, trace fossils and ripple marks are seen in the Dakota.  Cross section below from the James St. John website. 

 

This is a road-cut at the top of the hogback showing the Cretaceous/ Jurassic boundary. Note the globular concretion in the Morrison.

 Morrison

 

This therapod track was found in a boulder and moved to its current location. It maybe from a young Allosaurus.  Therapods were three-toed carnivores and are the distant ancestors of modern birds; in fact, some had feather-like skin covering.

This Allosaurus is a typical three-toed, carnivorous therapod.

This bulge is probably a sauropod foot print (possibly an Apatosaurus), seen in cross-section.  Sauropods had very long necks, long tails, small heads and four thick, pillar-like legs.

The Apatosaurus is a typical sauropod, much like the famous brontosaurus.

A rare velociraptor (commonly shortened to "raptor") footprint.  They were related to the related to the therapods. This is one of only twelve raptor sites in the world. 

Bones of a sauropod dinosaur, possibly an Atlantosaurus (similar to the Apatosaurus above).

 Dakota

Iguanodontid and theropod dinosaur tracks; stained gray with charcoal for easier visibility. Iguanodontids were large herbivores which were both bipedal and quadrupedal. 

An Iguanodon.

Crocodilian claw scratch marks

 

Ripple-marks made in shallow water. 

Invertebrate trace fossils: burrows made by invertebrates in the soft shoreline mud. 

These guys were pretty huge !!!!

So what on earth is Sharon sitting in?  We are in the Blanco River bed if that helps. 

And here are more:

Does this give you a clue?

The size looks right

Sometimes they are enhanced by the river water

And they usually form a linear pattern

By now you have guessed. Sauropod (Greek = "lizard foot") tracks.   These are in the Glen Rose formation of the Lower Cretaceous.

The Glen Rose is a widely distributed shallow-marine formation as indicated both by ripple marks and abundant marine invertebrate fossils.

These types of tracks are not that uncommon in Texas but these are conveniently close to Austin and San Antonio.  How do you get there:

Take FM 1623 west of Blanco. In just over three miles you pass the intersection to CR 103 (Trainer Wuest Rd.) on the left.  Shortly thereafter, there is safe and convenient parking on the side of the road.   Walk back to Trainer Wuest Rd. and take it down to the river.  If it is safe to do so, you can then hike the river bed east (towards Blanco) for a few hundred yards and should easily see plenty of tracks in the exposed Glen Rose formation. Its then probably worth backtracking to the Trainer Wuest Rd. river crossing and keep on going to the west for half a mile or so.  There are more tracks to see on this stretch. 

Some other thoughts:

1. Never, ever hike the river bed if the water level or flow rate creates an unsafe situation. 
2. This blog entry does not imply that it is legal to access the river bed in Blanco County. I have no clue about private land/river rights.
3. The dirt road (Goldwin Smith Rd.) on the south side of the river is definitely private property. 
4. See last week's blog entry for info. about the therapod (carnivore) tracks on the San Gabriel River. 

  

 

Covid Mitigation Activity: Cretaceous Park

So, this week’s Covid Mitigation Activity was to take a visit to Jurassic Park …. actually, Cretaceous Park in our case.  About a half mile west from the Hwy 183 bridge that crosses the South Fork of the San Gabriel River near Leander, lies twelve or so dinosaur footprints embedded in the Glen Rose formation of the river bed.

Based on the shape of the three-toed prints, geologists believe they may have belonged to a huge carnivore called the Acrocanthosaurus which is a theropod dinosaur that existed in the Early Cretaceous, about 120 million years ago. These guys reached about 40 ft. in length and weighed up to six tons.  

 Seeing them dry is not as impressive as when wet.  That/’s easy as there is plenty of water to dampen them. The circular ring around a couple are man-made; perhaps a failed attempt at removal?

There are also supposed to be some faint sauropod tracks closer to the 183 bridge but we did not see those.  As vaguely round depressions, they blend easily into the surrounding erosional features of the river bed. These fellows were giant, long-necked herbivores, similar to the once-named “brontosaurus”.

There are a few palaeontologists that question the Acrocanthosaurus tracks’ authenticity. “Poor farmers in the region during the Great Depression learned they could sell the chiseled-out tracks for significant profit to visiting tourists and paleontologists. And when the supply got low, they learned some innovative ways to boost the inventory”.  However, the Glen Rose formation is famously prolific for dinosaur tracks throughout Texas including Dinosaur Valley State Park. 

I, for one, will continue to imagine this huge creature lumbering down what is now the river bed, looking for a tasty herbivore for dinner.

 Getting there is easy.  

• Set your GPS for this street address:  601 S Gabriel Dr. Leander, TX 78641.  https://goo.gl/maps/vXVDy95Ux2Aw1Hk36
• Park in the obvious space between the north and south 183 carriageways.
• Walk down to the river on either side of the parking lot.  Turn left (west) and walk upstream for about 0.6 miles
• The theropod tracks are here: https://goo.gl/maps/ft419fUVZqk or 30°37'01.1"N; 97°52'05.8"W. 
• If the river is flowing fast or the water level is high, don’t bother going. It could be dangerous and the tracks are in the river, so you would not be able to see them anyway.
• The river bed and banks are public but the property on either side is private.

Enjoy !!!!

The Birds Have it Made

When a certain someone visited the hummingbird festival in Fort Davis, she began to have ideas for a Cadillac bird perch. .  All she needed was a dead one of these:

Once a dead Century Plant is obtained, the next step is to dig a hole in the back yard, pour in quick-dry concrete and stick in a cut piece of rebar. Allow to dry.

Now wack a piece of aluminum tube into the trunk:

...... using a special drill bit + extension if the trunk has not yet rotted away:

If the stalk is cracked or broken it can be secured with hose clamps and/or zip ties:

Lastly, up-end the stalk and slide the aluminum tube over the rebar:

And Bob's Your Uncle (whoever Bob was).