Sometimes when a question is posed, there’s a simple answer. Other times, questions spark inquiries that lead you down a rabbit hole lined with mystery and legend. A recent fact check about the elevation of Haystack Mountain triggered such an inquiry. This investigative path uncovered footprints of dinosaurs that frolicked on the beaches of the Front Range, and the tomb of Chief Niwot, which according to legend sits atop Haystack Mountain, its 500-foot peak representing the elevation of Left Hand Creek 100,000 years ago.
The inquiry started with a phone call from a reporter working on a story about our cheeses, who wanted to confirm the elevation of Boulder County’s Haystack Mountain. Our marketing director John fielded the call and he chuckled to himself, because as anyone in Boulder County can tell you, it’s a matter of a few hundred feet high. After some quick Googling around, he learned that there’s not much concrete info on our company’s namesake, Haystack Mountain. There is, however, a slew of other locales with the same namesake: an elite Vermont ski resort, a mountain in Idaho’s Portneuf Range, an East Coast crafts school, and an 11,000-foot Colorado peak near Kremmling.
Amid the digital clutter, there was an article written by local geologist Suzanne Webel, a 20-year veteran of the petroleum industry who lives on an 80-acre farm in the triangle between Boulder, Lyons, and Longmont. John contacted Webel and had some follow-up questions. “Well, a lot like geology, it’s literally a long story,” Webel chuckled. Webel says that Haystack’s bulbous shape gave Boulder County’s first settlers pause. “The first farmers who arrived in the area were worried that Haystack Mountain was a volcano. It’s actually a flood-washed structure that used to be part of Table Mountain,” she said.Webel’s original article details the geological structure of the Table Mountain area, but we were focused on Haystack “peak” itself. John commissioned Webel (with cheese, naturally) to dive deeper into the geology of Haystack Mountain. Webel accepted the challenge with curiosity and moxie, and produced an amazing story of rising and disappearing mountain ranges; vast seas containing dinosaurs, tree ferns, and clams; glaciers and deltas; stream capture and inverted topography.
To research her Haystack report, Webel went to the CU geology library and consulted with current professors on the matter. ”I had some nagging questions,” Webel said, “and this paper caused me to do more research on something I wanted to know more about.”
From a historical and cultural standpoint, the land surrounding Haystack Mountain is entrenched in Native American and U.S. history. In the early 1800s, Chief Niwot (meaning “Left Hand”) and his Arapahoe tribe chose this area as their winter home. Haystack Mountain served as a high lookout for small herds of buffalo, its sunny slope provided protection from harsh winds, and Left Hand Creek ran with fish and clear mountain water. In 1858, history reports that Chief Niwot met the first settlers coming into the region, and many more followed.
Eventually, with the continuing unrest between the settlers and the Indians, Chief Niwot moved his tribe to eastern Colorado near Sand Creek. There at the Battle of Sand Creek, Chief Niwot was killed. According to legend, members of his tribe who escaped death in the massacre brought his body back and buried him on his beloved Haystack Mountain.
Geologically speaking, “cute little” Haystack Mountain is an erosional outlier whose days are numbered, at least in the way geologists look at time. We invite you to read Webel’s full report on the geological structure of Haystack Mountain; it’s a fun and fascinating read that speaks to both the layperson and the well-versed geology buff.
GEOLOGY OF THE HAYSTACK MOUNTAIN AREA
by Suzanne Webel
Have you ever wondered about the geology of Haystack Mountain? It’s an amazing story of mountain ranges that rose up, disappeared, and then rose up again; vast seas containing dinosaurs, tree ferns, and clams; glaciers and deltas; stream capture and inverted topography. Hang on and enjoy the ride!
The Analogy of a House
While Table Mountain and Haystack Mountain dominate much of the viewscape along the east side of the Front Range of Boulder County today, let’s look at how they fit into the geological “big picture.” Sometimes it’s useful to think of the whole assemblage of rocks as a house.
The basement of the house in our part of Colorado is composed of ancient Precambrian granites approximately 1.5 billion years old. The basement has undergone many episodes of uplift and subsidence, with a big one occurring about 370 million years ago forming a mountain range in approximately the same location as today’s Rockies, called the “Ancestral Rocky Mountains.”
The First Floor
The first floor of our geological house consists of relatively hard rocks that range in age from Permian to Jurassic. The Ancestral Rocky Mountains eroded quickly (in the otherwise relatively slow geological scheme of things), shedding large amounts of coarse debris eastward, which was deposited in deltas and alluvial fans. These sediments later hardened into the red conglomerate we call the Fountain Formation, which is well-displayed as Boulder’s Flatirons and at the Hall Ranch Open Space. Subsequent, finer-grained sediments were deposited mostly as sandy beaches with intervening mudflats. The reddish Lyons sandstone is used to face the buildings at the University of Colorado. These formations, like most sedimentary rocks, were originally deposited in a horizontal position.
The Second Floor
The Cretaceous period deserves the entire second floor of our geological house (these rocks are very thick here so the house has peculiar proportions). A vast seaway extended all along the Rocky Mountain front from Canada to Mexico. Dinosaurs frolicked on the beaches and left their footprints in the Dakota sandstone outcrops. Clams grubbed around in the mud and sometimes even got stepped on by the dinosaurs. Occasional offshore reefs resulted in limestones like the Niobrara, which is now being mined for cement at Dowe Flats east of Lyons. The Cretaceous deposits are best known around Haystack Mountain as the black shales of the Pierre Formation, which can reach 6,000 feet in thickness. The Pierre shale is also known for its swelling clays, which can cause engineering headaches in foundations, roads, and bridges. Occasionally the marine muds gave way to narrow sandy beaches, resulting in thin layers such as the Hygiene Sandstone member that intertongue with the thick black shales of the Pierre Formation.
Renewed uplift of the Rocky Mountains about 70 million years ago resulted in folding and faulting of the entire house of cards. If you were allowed to go up on Table Mountain (but you can’t, since it’s closed to the public) you might be able to see a small anticline (where the rocks tilt away from each other) and syncline (where the rocks tilt toward each other), with a small fault in places between them. These forces may still continue today, as friction along faults creates warm springs such as those at Rabbit Mountain, whose waters were piped all the way to Hygiene to supply the sanitarium there. A flurry of oil drilling just after the turn of the century between the Lake Valley Golf Course and Haystack Mountain discovered geothermal hot water (300 degrees Fahrenheit at 1500 feet), which still flows to the surface under artesian pressure and creates small wetlands that never freeze, making the area a prime winter haven for wildlife. The closest oil production to Haystack Mountain is about three miles south, in the very small, now-abandoned Boulder Oil Field.
Most of us live on the roof. The Quaternary period was marked by another major outpouring of coarse sediments that were shed eastward from the mountain front. Dinosaurs had given way to woolly mammoths and saber-toothed tigers. Glaciers covered much of North America in the Pleistocene epoch. Sediments were deposited by huge ancestral rivers that make today’s creeks (Boulder, Left Hand, and St Vrain) appear puny in comparison. Deposited about 100,000 years ago, the giant outwash plains from these rivers contain a hodge-podge of rocks of all types, from whatever source happened to be uphill: granite, gneiss, quartzite, limestone, and sandstone. The oldest, barely-consolidated gravels and conglomerates of this period in our area (collectively called the Rocky Flats alluvium) rest directly on the Pierre Shale.
Generally younger still is the Verdos Alluvium, which is marked by brown sand and gravel, with pebbles, cobbles, and boulders that are weathered and decomposed. Caliche, a hard, calcareous cement, fills old cavities and coats many of the stones, making this formation resistant to erosion (and to agriculture!). The Verdos comprises some of the topographic benches on the west side of Table Mountain, as well as “holding up” the mesa itself. Just east of Table Mountain the soils contain a lot of boulders that are erosional remnants of the Verdos Formation, which may once have extended as far east as Longmont.
Other places to see these young pediment formations are the top of the NCAR Mesa, the mesas of Boulder Valley Ranch Open Space, Gunbarrel Hill, and Rocky Flats along Highway 93 toward Golden. We’ll lump them all together and call them Quaternary gravels (Qg). They, in turn, are overlain by unconsolidated miscellaneous silt, sand, and more gravels, mostly alluvial in nature, that were deposited “yesterday.” We’ll call these very recent sediments Quaternary alluvium, or Qal.
Pirates on the Roof!
Did you know that there have been pirates throughout geologic history? In this area, the big rivers coming out of the mountains deposited gravels during glacial periods, and they cut down into the shales when the water ran clear during interglacial periods. The glacial rivers had to snake around to avoid the piles of debris they had just deposited, and sometimes they would jump their banks so violently they would end up in a completely different location… and then, thousands of years later, they might jump back to their original position. There is a subtle example of this process just north of Table Mountain, where about 90,000 years ago Left Hand Creek exited the mountains and ran along what are now Toll Gate Ditch and Lykins Gulch. Then it abandoned that channel and “beheaded” its own pediment mesa to find a better channel — just south of Haystack Mountain — where it has been ever since. In this way, various flood deposits would frequently intertongue with each other, making determining their relative ages a difficult process. Some geologists at CU have recently developed a new process of determining the absolute age of these recent sediments using Beryllium decay, and they are now going around the area painstakingly trying to unravel the chronological history in the rocks.
Sometimes small rivers eat away slowly and sneakily at the slopes nearest them, and eventually they might succeed in grabbing their entire watershed from a completely different river. This process is called “stream piracy.” There is an example of stream piracy taking place today, along the southeast corner of Table Mountain, where a tiny unnamed creek is eating away at the face of Table Mountain. Farther east, out toward Longmont, it’s called Dry Creek…..
The Chimney: Haystack Mountain
So maybe you’ve guessed it by now…. Yep, believe it or not, the very top of Haystack Mountain is all that is left of a vast sheet of Rocky Flats / Verdos Alluvium that once used to connect it directly to Table Mountain. Two tiny streams – Dry Creek and a mostly dry-gulch tributary of Left Hand Creek — have eroded away the resistant caprock of alluvium and are now quickly cutting down the shale layers between them, leaving just a gentle topographic saddle along Oxford Road and Ouray Drive. Some day soon (geologically speaking), the saddle will get lower and lower until it disappears entirely. Which stream will be the pirate and which the victim – Left Hand Creek or Dry Creek? Only geologic time will tell.
At the same time, although there is still a tiny bit of caprock protecting it, erosion is eating away at Haystack Mountain from all sides…. So it too, will eventually just disappear.
But here the “house” analogy ends. Unlike a chimney that has heat going up inside it, this cute little pinnacle called Haystack Mountain is an erosional outlier, not a volcano!
One Last Amazing Thing
So, have you noticed that you’re (presumably) standing on the youngest rocks around, at the bottom of a big wide valley in Boulder, Niwot, or Longmont, yet you’re looking up at Table Mountain and Haystack Mountain, which are somewhat older? “Inverted topography” occurs when low areas of a landscape have been filled with sediment that hardens into material that is more resistant to erosion than the surrounding material. Differential erosion then removes the less resistant surrounding material, leaving behind the younger, more resistant material which then forms a ridge or a mesa where previously there had been a valley. The erosion-resistant rocks on the top of Table Mountain and Haystack Mountain represent the elevation of Left Hand Creek 100,000 years ago when they were deposited at the bottom of a big valley, but today they are the highest features for miles around and the creek is 500 feet below its original level. Now that’s geology in action!
Looking at a Big Slice of the Rock Record
Imagine that you have just dug a trench about 3,000’ deep along an imaginary line from Heil Valley Ranch on the northwest, across Table Mountain and Haystack Mountain, to the Diagonal Highway at IBM on the southeast. Climb down into the trench and clean off all the rock dust and mud so you have a clean, shiny wall to look at. Face roughly north. By projecting where you are standing into this imaginary trench, you can pretty well predict what kind of geology lies under your feet.