Dear Readers: I did not get an answer as I had planned for this week, so I reached into the archives for a column that many of you will find interesting. Last week’s answer about the antennas on Table Mountain west of Longmont reminded me of another answer, from April of 2016, about Haystack Mountain.
Note that the dates provided in this answer are now almost six years off. Here it is:
Hi Johnnie: Ever since moving here three years ago this month, we have been intrigued with the conical-shaped mound of land west of Niwot. It seems so out of place in the flat land in which it rises. We have been told by one friend that it is an Indian mound and by a Niwot resident that it is called Haystack Mound.
Can you please enlighten us about its history? Thank you so much for all of your good information about our area. — GL
Hi GL: It’s not an Indian mound. It’s not any sort of mound.
It’s not a volcano, either, something that the first farmers in the area feared.
“Most of the early settlers assumed it was a volcano and didn’t want to settle anywhere near it,” said Suzanne Webel, a Boulder County geologist who within the past year completed an essay on Haystack Mountain, commissioned — with cheese — by the goat dairy that derives its name from the geologic structure.
What is now Haystack Mountain was once part of Table Mountain, said Webel, who has lived in Boulder County for 42 years.
Table Mountain is the plateau just northwest of Haystack Mountain, identifiable by the two large dish antennas on its northern flank.
GL, here’s my simplified version of the events that led to the creation of Haystack Mountain, gleaned from Webel’s essay and from my conversation with her. As Webel said, “It’s not clear cut what happened.”
About 100,000 years ago, long before the invention of Google, rivers were carrying vast amounts of gravel and conglomerates off the mountains and onto the gentle slopes at the base of today’s foothills. Those rocks — known as the Rocky Flats Alluvium — became a hardened layer on top of softer rock.
Streams then began cutting their way through the hard layer and into the softer layers, leaving behind tables, or mesas, such those you see along the Front Range.
At some point in that deep past, a river or stream began to cut away the southeast portion of Table Mountain, opening a wider and wider gap between the bulk of the plateau and the much smaller Haystack Mountain. There’s even a saddle between the two mountains, Webel said.
Haystack Mountain has held its shape thanks to a remnant of the hard layer at the top, called a caprock. But like Table Mountain, Haystack Mountain is slowly eroding, because of rain, snow and wind.
How much longer will we have Haystack Mountain?
After first being hesitant to narrow it down to anything more specific than “it could be a hundred thousand years, it could be a million,” Webel provided a more specific number in a follow-up email.
“Regionally the long-term erosion rate seems to have averaged between 0.1 mm/year (and) 0.9 mm/year …,” she wrote. “Anyway, if we try an average of 0.5 mm/year, and if we assume that the tip of Haystack Mountain is 300 feet above the valley, and convert 300 feet to millimeters, it’s 91,440 mm high. That means Haystack Mountain would disappear completely in 182,880 years. Exactly.
“Ha! … Nothing in geology is ever that clear-cut, of course, but we can still engage in fun little speculations.”
I wouldn’t worry about being wrong on that one.
Send questions to johnnie@times-call.com
