Tilted strata beneath the bridge. (photo by Robert Titus)
It’s summer at last, and time to get out and do things. We are fortunate to live in such a scenic region. There is so much to see. We are double lucky; we have, in recent years, added a very fine vista to our Hudson Valley. That is the Walkway Over the Hudson pedestrian bridge which links the west bank of the river with Poughkeepsie. Officially it is the “Walkway over the Hudson State Park,” but whatever you would like to call it, it is a marvel.
The bridge was originally built in 1889 as a steel cantilever railroad bridge and it served that way for decades. It was considered an engineering marvel in its day and for a long time it was the only cross Hudson bridge south of Albany. Use declined after 1960, and it closed for railroad traffic in 1974. Then it lay unused for a quarter of a century. I guess it was a gigantic white elephant during that time, but then somebody got smart. In the late 90’s plans were developed to turn it into a pedestrian and bicycle bridge. All that came to fruition in 2003. Since then it has been open to the public for recreational enjoyment. You can walk from one side to the other and soak in the views of the Hudson Valley to the north and to the south. It’s well worth the effort, and I think it was well worth the money they spent.
But, this is alleged to be a geology column and I am not supposed to be singing songs about bridges, am I? How do I justify all this? Easy — I just had to go and look around. My wife and I went down to the west end of the bridge and hiked out onto it last summer. I brought a camera and resolved to find something I could write about. It didn’t take long.
We hiked out only a short distance and I looked off to the south and there was my first good dose of geology. It was a sequence of stratified rocks doing something that you won’t see in the Woodstock vicinity. These strata showed a pronounced dip to the north. They, hundreds of millions of years ago, got caught up in one of the several mountain building events that have influenced the whole Appalachian realm. It might have been the Appalachian Orogeny itself, which occurred when Africa collided with North America. That happened a quarter billion years ago but the results are still visible. The crunch that resulted likely caused the folding that I was looking at. If you go down, take a good look and appreciate what you are viewing. Imagine, for a moment, the energy that went into lifting and tilting such a massive thickness of stratified rock. It’s a wonderment!
Wonderful, informative article, Robert. I’ll be sure to look for the stratified rocks on my next trip over the bridge. I’d like to read more… could you recommend a book that deals specifically with this area? Thank you.