Welcome to my Earthcache! An Earthcache is a special type of geocache where there is no container to find - instead you are looking for a unique geological feature of the area and need to answer questions, as well as posting a picture, in order to claim the find. This EarthCache takes you to the Quartz Conglomerate boulders in Rock City Park, Olean NY. These unique rocks are part of a process from millions and millions of years ago, and they have been shaped by a variety of processes into what you see today. This particular earthcache looks to explore the make up of the conglomerate - how all of the quartz, mud, clay and other materials formed to create this geological wonder.
Please Note: Rock City Park is a private attraction that is open from May to October annually from 9am until 5pm. The park may close early in case of inclement weather or private events within the park. There is a fee of $8.00 per adult/$5.00 per child to enter the park. This Earthcache has been placed with the permission of park manager Nate Smith. A big thanks to bigguy14760 for obtaining permission from Nate and assisting with the creation of this earthcache.
EARTHCACHE REQUIREMENTS
As with all of my ECs, I am not looking for PhD thesis level responses, but I am hoping that you take some time to enjoy the area and learn something new. Please include a list of all cachers with your answer, if answering for more than one caching name. There is no need to send individual answers.
To claim a 'find' for this Earthcache you must answer the following questions and send your answers in a message or email to the owner using the link at the top of the page. You can log your find with a photo at GZ. Send your answers to the tasks. I will be in contact if there is a problem, no need to wait for a response as long as the required photo is included in your log.
Observational Task
At GZ, you should be standing at the bottom of Rock City Park, staring up at towering cliffs of quartz conglomerate. You can access this area by one of two ways - a steep metal staircase from the top, or by taking the trail "backwards". In either case, this area is not recommended for those who are mobility challenged.
Questions to Answer:
-
Observe: Examine a rock face and describe the color and texture of both the pebbles and the matrix. Identify at least one quartz pebble and describe its shape and luster. Based on the description, how do you know that this is actually made of quartz (beyond "because you said so")?
-
Describe: Try to remove one of the pebbles from the conglomerate with your fingernail. Why do you think the matrix here is able to bind the pebbles so tightly?
-
Describe: What can the size and roundness of the pebbles tell you about the energy of the water that deposited them? Why do you think quartz is more common in older river deposits as opposed to new rivers?
-
Photo: Include a photograph of yourself, your GPS, a signature item, thumbs up, etc at your favourite formation within rock city park. You do not need to show your face in the photo, but your photo must be unique to you. In the event of group photos, please have each member of your group upload the photo (each log should have at least one photo uploaded).
EarthCache Description
At Rock City Park, you're standing on the remnants of a powerful prehistoric river system. These rivers carried quartz-rich sediments that eventually formed the quartz conglomerate, a rock type known for its striking pebbled texture. This EarthCache explores the full lifecycle of this rock—from mineral formation to sediment deposition and final lithification—while helping you identify the rock’s components in the field.
What is Quartz and How Does It Form?
Quartz (SiO₂) is one of Earth’s most abundant and durable minerals. It forms in a variety of geological environments, primarily through:
-
Crystallization from molten rock (magma): Quartz often crystallizes in igneous rocks such as granite.
-
Precipitation from silica-rich fluids: Quartz can also form in sedimentary environments when dissolved silica precipitates in spaces between grains, acting as cement.
Over time, weathering breaks down quartz-bearing rocks. The resulting quartz grains and pebbles are then transported by water and become incorporated into sedimentary deposits—like those at Rock City Park.
What Is Quartz Conglomerate and How Does It Form?
Quartz conglomerate is a sedimentary rock made of rounded quartz pebbles embedded in a finer-grained matrix. It forms through a multi-step geologic process:
1. Weathering and Erosion - Quartz is a highly durable mineral that resists chemical weathering. As surrounding, less-resistant rocks (like feldspar-rich granite or schist) break down, quartz pebbles remain intact and are transported downstream by rivers and floodwaters. The repeated tumbling action during transport rounds off the edges of the pebbles.
2. Transport and Sorting - As rivers slow down, they lose the energy needed to carry larger sediments. The quartz pebbles drop out of suspension and begin to accumulate, often in gravel bars or river deltas. The varying energy levels of these environments sort the particles by size and weight.
3. Deposition - In the case of Rock City Park, the quartz-rich sediment was deposited during the Late Devonian to Mississippian periods in what was likely a braided river system. The sediments settled in thick beds that buried and compacted over time.
The Matrix: What Holds the Conglomerate Together?
The matrix is the finer material that fills the spaces between the large pebbles. In quartz conglomerate, this matrix typically includes:
-
Fine-grained quartz sand, washed in with the pebbles.
-
Clay minerals, derived from the weathering of feldspars and micas upstream.
-
Silica cement, which precipitated from groundwater carrying dissolved silica. Over time, this cement chemically bonded the grains together, forming a hard, cohesive rock.
In some samples, iron oxide gives the matrix a reddish tint, a sign of oxidizing groundwater present during lithification. Keep an eye out for this red staining as you wander through Rock City Park, and try to identify a few examples of iron oxide within the matrix.
Field Identification: Recognizing Quartz Conglomerate
When you examine an outcrop at Rock City Park, look for these features:
-
Rounded quartz pebbles, typically white to gray, sometimes pink.
-
Hard matrix that is lighter in color and visibly cemented. Keep in mind that the matrix may have weathered over time, giving it a darker or black appearance - try to find a sample that has not be affected by weathering for a representation of the true colour.
-
Poor to moderate sorting, with pebbles and smaller grains packed together.
-
No visible layering like in shale or sandstone; instead, a blocky texture that does not appear to have formed in distinct layers.
References