While geocaching in the area, I came across a unique geologic display which showcases different geologic ages and their associated rocks which are found around the Mojave desert. What is particularly interesting is that these rocks are casts of rocks found locally that contain dinosaur footprints! Yup, you heard that right! While these are not the real deal, they are here for public display to learn about the dinosaurs that once called this area home.
While standing on the sidewalk (with the intersection of Virginia and Barstow to your left), from left (east) to right (west) is oldest to youngest.
Jurassic Period (199.6 million to 145.5 million years ago)
The Jurassic period marks the middle of the age of the dinosaurs. From Britannica:
The Jurassic was a time of significant global change in continental configurations, oceanographic patterns, and biological systems. During this period the supercontinent Pangea split apart, allowing for the eventual development of what are now the central Atlantic Ocean and the Gulf of Mexico. Heightened plate tectonic movement led to significant volcanic activity, mountain-building events, and attachment of islands onto continents. Shallow seaways covered many continents, and marine and marginal marine sediments were deposited, preserving a diverse set of fossils. Rock strata laid down during the Jurassic Period have yielded gold, coal, petroleum, and other natural resources.
During the Early Jurassic, animals and plants living both on land and in the seas recovered from one of the largest mass extinctions in Earth history. Many groups of vertebrate and invertebrate organisms important in the modern world made their first appearance during the Jurassic. Life was especially diverse in the oceans—thriving reef ecosystems, shallow-water invertebrate communities, and large swimming predators, including reptiles and squidlike animals. On land, dinosaurs and flying pterosaurs dominated the ecosystems, and birds made their first appearance. Early mammals also were present, though they were still fairly insignificant. Insect populations were diverse, and plants were dominated by the gymnosperms, or “naked-seed” plants.
Plistocene Epoch (2.58 million to 11,700 years ago)
The Plistocene epoch marks the beginning of the ice ages. From Wikipedia:
The Pleistocene, (often referred to colloquially as the Ice Age) is the geological epoch that lasted from 2.58 million to 11,700 years ago, spanning the Earth's most recent period of repeated glaciations. The end of the Pleistocene corresponds with the end of the last glacial period and also with the end of the Paleolithic age used in archaeology.
At the end of the preceding Pliocene, the previously isolated North and South American continents were joined by the Isthmus of Panama, causing a faunal interchange between the two regions and changing ocean circulation patterns, with the onset of glaciation in the Northern Hemisphere occurring around 2.7 million years ago. During the Early Pleistocene (2.58–0.8 Ma), archaic humans of the genus Homo originated in Africa and spread throughout Afro-Eurasia.
The end of the Early Pleistocene is marked by the Mid-Pleistocene Transition, with the cyclicity of glacial cycles changing from 41,000-year cycles to asymmetric 100,000-year cycles, making the climate variation more extreme. The Late Pleistocene witnessed the spread of modern humans outside of Africa as well as the extinction of all other human species. Humans also spread to the Australian continent and the Americas for the first time, co-incident with the extinction of most large-bodied animals in these regions. The aridification and cooling trends of the preceding Neogene were continued in the Pleistocene. The climate was strongly variable depending on the glacial cycle, with the sea levels being up to 120 metres (390 ft) lower than present at peak glaciation, allowing the connection of Asia and North America via Beringia and the covering of most of northern North America by the Laurentide Ice Sheet.
Quaternary period (2.58 million to today)
And finally we have "recent" or the Quaternary period. From Britannica:
The Quaternary begins 2,588,000 years ago and continuing to the present day. The Quaternary has been characterized by several periods of glaciation (the “ice ages” of common lore), when ice sheets many kilometres thick have covered vast areas of the continents in temperate areas. During and between these glacial periods, rapid changes in climate and sea level have occurred, and environments worldwide have been altered. These variations in turn have driven rapid changes in life-forms, both flora and fauna. Beginning some 200,000 years ago, they were responsible for the rise of modern humans.
The Quaternary is one of the best-studied parts of the geologic record. In part this is because it is well preserved in comparison with the other periods of geologic time. Less of it has been lost to erosion, and the sediments are not usually altered by rock-forming processes. Quaternary rocks and sediments, being the most recently laid geologic strata, can be found at or near the surface of the Earth in valleys and on plains, seashores, and even the seafloor. These deposits are important for unraveling geologic history because they are most easily compared to modern sedimentary deposits. The environments and geologic processes earlier in the period were similar to those of today; a large proportion of Quaternary fossils are related to living organisms; and numerous dating techniques can be used to provide relatively precise timing of events and rates of change.
Fossilized Footpints
For some animals, their footprints can become preserved but only under certain conditions. The sediment the footprints are made in have to be very soft, like silt or mud along a river or a lake. It has to have a fast burial, meaning sediment must be deposited ont top of it to preserve it quickly. And then it must harden before part of the rock is errored way, leaving behind either a cast or a mold (depending on what erodes away and what is left behind).
Works cited
https://www.britannica.com/science/Jurassic-Period
https://www.pinterest.com/pin/scene-in-a-jurassic-period-forest-by-kim-thompson--437271445061127343/
https://ceipsanpablomurcia.com/index.php/Pleistocene-epoch-The-last-ice-age-3498142.html
https://www.floridamuseum.ufl.edu/fossil-horses/time-scales/pleistocene/
https://en.wikipedia.org/wiki/Pleistocene
https://www.britannica.com/science/Quaternary
https://www.nps.gov/dena/learn/nature/making-dino-prints.htm
1. "Geologic Footprints" on the first line of your email AND list all geocaching names of your party so I can match your answers to them. If you all want to learn something, I would prefer each cacher send me individual emails in the spirt of earthcaching.
2. Take a photo of your favorite dinosaur footprint using some sort of scale. Geologists often use coins, GPS', pens, shoes, notebooks, ect. You might want to be creative in what you use for your scale, however, the scale that you choose is entirely up to you. Make sure your photo is close enough to capture an entire footprint so that it is clearly seen. This photo MUST be uploaded to your "found it" log. Please do not send any photos through the message center as Groundspeak compresses images. Each log MUST have a unique and different photo. No two logs may contain the same photo.
For the Jurassic segment:
3. Count the number of dinosaur footprints in the display. You do not need to be exact. Just give me a ballpark number for each section.
4. Describe the (a) textures, (b) range of colors and (c) relative size of the footprints.
For the Pleistocene segment:
5. Count the number of dinosaur footprints in the display. You do not need to be exact. Just give me a ballpark number for each section.
6. Describe the (a) textures, (b) range of colors and (c) relative size of the footprints.
After you visit all segments:
7. Are these fossilised footprints molds or casts? How can you tell?