This Earthcache is located at the Plymouth Rock public canoe landing along the Upper Iowa River.
Rising before you at this public canoe launch are some tall limestone pillars. The Galena Limestone here is an organic sedimentary rock that was formed layer upon layer in calm shallow seas during the Ordovician period (45-400 million years ago) from the skeletal remains of marine life.
Why do we find these Pillars here?
During the last 2.5 million years, parts of North America were covered on and off by glaciers.
Multiple advances by glaciers have scoured the ground down and flattened the landscape, picking up all kinds of debris-silt, sand, gravel and boulders as they moved. That debris, known as glacial drift, was left behind when the glaciers retreated.
This part of Northeast Iowa is known as “The Driftless Area”. It was missed by the most recent glaciation with the glaciers advancing and retreating around, but not over, this region. So, what you see here was not ground down and covered by glacial drift.
The deep, rugged valleys, exposed bedrock and these towering pillars are here because the rivers and streams of the area have had millions of years to carve and erode the underlying bedrock, their work never erased by the flattening of the land and the deposition of new sediment.
Before you can log a “Found It”, you must send your answers to the following questions to the cache owner:
- Estimate the height of the closest rock pillar to your left.
- What type of rock is it?
- Describe the pillar; shape, colors and texture
- Do you see any rock layering across the River indicative as to how it formed?
- What was the primary erosional force that exposed and shaped these pillars?
Please post a picture of yourself or a personal belonging at the site.