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Step Into The Early Jurassic

A cache by CTGEOSURVEY Send Message to Owner Message this owner
Hidden : 11/15/2006
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Geocache Description:

The Connecticut Valley has a long history of fossil track discoveries. Outstanding specimens uncovered in 19th century brownstone quarries found their way into museums throughout the world. A new chapter in the history of such discoveries was written in 1966 when hundreds of tracks were exposed in Rocky Hill. This site became what is now Dinosaur State Park. The trackway, preserved in place, is a Registered Natural Landmark by the National Park Service.

Purpose: This EarthCache is created by the Connecticut Geological and Natural History Survey of the Department of Environmental Protection. This is the first in a series of EarthCache sites designed to promote an understanding of the geological and biological wealth of the State of Connecticut.

Supplies: You will need a measuring tape and park trail map. Spoilers may be included in the descriptions or links.

Directions: Exit 23 off I-91 in Rocky Hill, CT. Follow park's signs east on West Street for approximately 1 mile. The park is directly off West Street. Watch for signs and a large geodesic dome. No cost to park and walk grounds. Admission into the Center is $10 for adults, $4 for children 6-12, Connecticut residents who are 65 or older, and children 5 and under are free.

History of the Park: In August 1966, bulldozer operator Edward McCarthy was excavating a rocky site for a state building. He turned over a slab of gray sandstone and saw something very exciting: six large, three-toed footprints.

Officials, local scientists and the media were notified, and the news of the discovery quickly spread. Many more tracks were uncovered and the site was fenced in and guarded. Within a few weeks officials decided to preserve the site as a state park. Two seasons of careful excavation resulted in one of the largest on-site displays of dinosaur tracks in the world.

Anyone who likes dinosaurs and plans to undertake the EarthCache should allow time to experience this incredible park. In addition to the 200 million year old fossil trackway there are interactive exhibits and the chance to cast your own dinosaur footprint to take home. Contact the park on materials you need to bring to makes these molds. There are several nature trails that are also of interest. One is the blue trail that hosts a board walk over a classic red maple swamp, a natural spring and at the furthest bench, traprock ridge views of a forested area below. The 10 acre arboretum surrounding the Exhibit Center have conifer trees and plants that grew in the Mesozoic Era, such as gingkos, dawn redwoods and magnolia.

Figure 1. Furthest bench along Blue Trail.

To log this EarthCache: Answer the 5 questions below, and send a photo from the given coordinates and number in their group.

Earthcache Logging Questions: Start your tour by examining the time-line walk. With the understanding that 12” equals 50 million years please answer the following questions:

1. What is the measurement in feet along the walkway between the emergence of dinosaurs and their extinction?

2. What is the measurement in feet along the walkway between the extinction of dinosaurs and the emergence of man?

3. Based on the answer to question 2 how many years does this measurement equal?

The rocks exposed at Dinosaur Park were formed about 200 million years ago. At that time Connecticut was located near a tropical to sub-tropical latitude, in the middle of a large super-continent created by plate tectonic processes. As such it was a long distance from a major ocean that could supply moisture to the climate: Connecticut's climate was semi-arid most of the time. That inference is supported by the recognition of numerous ancient soil horizons embedded in the rock layers. The paleosoils contain features called caliche found in modern soils that develop in semiarid climates. Thus, we infer that the ancient soils also developed in semiarid conditions that existed 200 m.a. The sedimentary rocks that contain ancient soils are reddish brown in color and are abundant along highway cuts in most the central part of Connecticut, from New Haven to the MA border. The reddish-brown color is caused by oxidation of iron contained within the sediment, caused by repeated desiccation of the sediment after its deposition. Exposure to air (oxygen) and water caused the iron minerals to rust, forming the reddish pigments.

Some layers, however, are gray and greenish colored, including those at Dinosaur Park. Examples of these outcrops can be seen about 100 feet towards the right of the Center’s entrance. These layers were deposited in large permanent lakes that were deep enough to have stagnant bottom conditions. That led to the preservation of organic matter in the lake bottom muds. The preserved organic matter captured all the available oxygen in the lake water and later in ground water and any iron in the sediment could not be oxidized. As a result the muds and sands now shale and sandstone have a grey and greenish grey color. That large, deep lakes could form into which abundant organic matter collected suggests a wetter climate during the time. Rock layers exposed elsewhere in the Connecticut valley are dominantly reddish brown in color, but are regularly punctuated with grey layers. This suggests that the climate rhythmically fluctuated between wet and dry conditions.

4. What is the name of the rock formation that contains the trackway? (Hint: answer to this question can be found on the plaque at the outcrop, which is to the north of the walk through geologic time.)

Now head towards the mold and casting site stopping at the retaining wall.

What are fossils? By definition a fossil is any remnant or trace of an ancient living organism preserved in rock. They are usually found in sedimentary rock or in some low-grade metamorphic rocks. We normally think of fossils as ancient shells or bones that are preserved in rock. But fossils can take many forms such as:

  • An actual remnant of the organism such as a shell, bone or other tissue, which may be preserved in ice, amber, silica or sedimentary rock;
  • A mold of the organism after the original hard part or tissue dissolved or decayed such as an impression of a leaf or shell;
  • In some places a mold had been filled with a different mineral, precipitated from groundwater solutions, making a cast of the plant or animal; and
  • In some places plant tissue is transformed into a film of carbon or the surface of an impression.

A final class of fossils is referred to as trace fossils, which include tracks, trails, burrows, and petrified fecal material. It is this last class of fossil that we will see at this park. Tracks are impressions made by a passing animal in soft sand or mud. Most tracks get destroyed shortly after they are created. Several things must occur for a track to be preserved in geologic materials. First, the surface upon which the track was impressed must be rapidly covered by another layer of sand or mud of sufficient thickness that track depression is filled in. Later the layers of sediment must be lithified or hardened into rock. In order for the rock to split at a later time and reveal the fossil track the layer immediately on top of the track must be of some different composition than the layer upon which the track was formed, thus forming a bedding plane. Beds break along their bedding planes when muddy sediment overlies sand or when mica concentrates along the bedding plane.

Figure 2. Mold and cast of Eubrontes track, the State Fossil displayed inside the Exhibit Center.

Notice the large stones that cap the retaining wall along the path straight ahead beyond (west of) the time-line walkway. These stones contain dinosaur footprints. But note that the footprints are all raised rather than being depresses as our experience show footprints to be. We find raised footprints when a rock slab is split off the ledge containing a normal track. The slab will have a raised foot print that exactly fits into the normal depression left on the rock forming the ledge.

5. The State Fossil is a dinosaur track whose skeletal remains have never been found. What is the name of the State Fossil?.


McHone, G. (2004). Great Day Trips to Discover the Geology of Connecticut. Perry Heights Press, Wilton CT. 206p. [Ch. 5 provides a concise, readable, history of Connecticut during the Mesozoic Era. Pages 115-120 describe Dinosaur Park.]

Bell, M. (1985). The Face of Connecticut. State Geol. & Nat. Hist. Survey of CT, Bull.110, 196p. [Contains several chapters, (ch. 2,6, & 8) written for the layperson, about geology of Connecticut.]

Coleman, Margaret (2005). The Geologic History of Connecticut’s Bedrock. State Geological & State Geol. & Nat. Hist. Survey of CT Natural History. Survey of CT, Special Publications 2, p. 29 see p. 22-24.

Trail Map for Dinosaur State Park: There are black and white trail maps at the Park. If you want to view or print a color map, click this .

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