Boom Hollow Cave EarthCache
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This wayside rest is closed between 10 pm and 6 am.
The wayside may also be closed in the spring due to flooding.
The St. Croix Boom is a National Historic Site located on the St. Croix River upstream of Stillwater, Minnesota. The site was founded by Stillwater lumber barons, including Isaac Staples, in 1856 after the demise of the original St. Croix Boom Company, which had operated a boom further upstream near Marine on the St. Croix, Minnesota. Staples and others purchased the Boom Company and moved the site downstream.
Timber harvested upstream was branded with the logo of the company that had harvested it. The logs were floated down to the boom, where they were sorted by the brands and delivered to the sawmills in Stillwater. The boom company collected a fee of 40 cents per thousand board feet (17 cent/m³) delivered.
The St. Croix Boom was a very profitable enterprise. In addition to a generous fee written into the company's charter and an efficient design that allowed it to be run by a small crew during slow periods, the sheer amount of timber that was being harvested made for high profits. During the 1870s, logs were frequently backed up for 15 miles (25 km) above the boom during mid-summer.
The St. Croix River valley provides the sedimentary geologist with some beautiful exposures of the “St. Croixian” series of rocks. These relatively level Upper Cambrian rocks throughout central and southern Minnesota. The four rock formations that make-up the St. Croixian have much in common. They are mostly sandstones with interbedded shales and siltstones. The greenish colored mineral, Glauconite is also common throughout the series, but is more rare in some layers than others. Some of the sandstones grade into sandy dolomite, and are fairly rich with fossils.
The Boom Hollow cave is located in the Franconia Formation bluffs in the sandy beach area at the southern end of the site. The Franconia Formation is the layer that contains the highest concentration of Glaconite, but at this location the bluffs are mostly white to yellowish-colored medium grain sandstone. A stairway leading down to the river is next to the parking lot and the cave opening can
be reached via a footpath that runs along the foot of the bluff and the river.
This cave is part of the original two- story cave that was used to store most of the food and supplies for the boom site settlement. I remember coming here in the 1970’s as a kid and looking up through a shaft at the upper level. Then, large boulders prevented you from going up to it though. Today, the upper level is currently behind the back wall. However, someone is always trying to dig under it, so a small hole is usually there. I have no idea how far back the actual cave wall is behind the modern wall. I just wish that there wasn’t so much graffiti on it. It takes away from the natural beauty of the cave and all of the memories I have coming here with my grandmother.
During the logging era, a cookhouse and supply store were located on top of the bluff directly above the cave and used the cave as a storeroom. A hole was cut into the roof of the cave, and a simple elevator was hoisted through the hole so that supplies could be moved from the cave to the cook shanty.
Walk about 100 feet downriver (towards Stillwater) from the cave and see how caves form, as a small stream appears out of the bluff and enters the St. Croix River.
To log this cache you must answer 3 questions. MAKE SURE TO BRING A TAPE MEASURE WITH YOU. You will not stick out by doing the two requirements as geology classes from all of the universities and colleges around visit this cave.
1. Take a photo of yourself/group and post it with your log
2. What is the length of the back wall?
3. What is the maximum height of the cave?
Email your answers to the questions, to me, using the link in my profile only. If your answers are not recieved by me in an appropriate amount of time, your log will be deleted. Photos are accepted and appreciated as long as the answers to the questions are not revealed. You do not have to wait for confirmation from me before logging this cache as completed. Most of all……learn……and enjoy the view.
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