The Walsen Dike

The Walsen Dike roadcut, located on Walsen Avenue on the north side of Walsenburg.

There are not too many places in the world where you can drive through a magmatic dike, but Walsenburg is one of them. Walsen Avenue cuts right through the Walsen Dike here, and the roadcut view is pretty amazing.

The dike was formed millions of years ago, when deep underground, a large, linear crack appeared in the earth's crust. This crack soon filled with molten magma, which eventually hardened and became the dike. Eventually, the dike was pushed up, or the crust above it eroded — or both — and the dike became a surface feature.

Looking at the picture of the dike, one sees sections of horizontal strata, probably formed at the bottom of an ocean. Here's what happened. The crack that originally formed occurred in what's called the Pierre shale. This geographical feature has horizontal lines when it's exposed in roadcuts or on the sides of hills or mountains.

When the magma filled the crack, creating the dike, it "baked" the shale on either side of the crack, essentially converting it into hardened rock like the dike itself. Sections of the shale then became a part of the dike itself, as we see in the picture.

There used to be a sign here that said, "HILL BLOCKS VIEW." However, it seems this sign has gone missing. Also, the one sign that is there indicates a left intersection, but coming southbound into town, the first intersection is the one that goes to the right, just north of First Choice Market.

Perhaps it would be a good idea to re-evaluate the signs in this area.