Roaming Colorado’s ancient seashores

I topped the familiar rise and half-walked, half-slid down the gray, soft-clay soil of Baculite Mesa on the lookout for fossil shells on one of Colorado’s ancient seafloors. On the rolling plain below, the cone-shaped hills called Tepee Buttes pointed skyward. The Tepee Buttes are nearly solid mounds of clam fossils, nested around the remains of a deep-sea methane seep analogous to ones in modern oceans where volcanic forces help belch new seafloor into existence. I would make my way there eventually, but in the meantime looked for reddish gray mounds of rock called concretions with evidence of shell parts nearby.

I soon found one and began carefully pulling it apart with rock hammer and trowel. It wasn’t long before my paleontologist’s heart warmed to the discovery of a clutch of mixed shells. Long, cone shaped Baculites shells that once housed squid-like mollusks rested near the shells of a kind of extinct clam called Inoceramus. I sat upon a bed of sediments that descend a mile deep beneath parts of eastern Colorado — the product of over 50 million years of deposition when relatively shallow oceans covered our state between 120 million and 67 million years ago.

Geologists and rockhounds could readily access such sites during the early days of Colorado’s statehood. Baculite Mesa, for example, was open range until the Homestead Act precipitated the formation of the Pueblo district in 1863. Several people now own the once beachfront property of the mesa. A group of amateur paleontologists, the Western Interior Paleontological Society (WIPS), cultivates good relations with the owners and have explored the site at least once a year for the past 26 years. My membership in the group helped inspire me to write several books that deal in some way with the fossils of North America’s Great Interior Seaway.

When I first moved to Wellington in the late 1970s you could still easily find fossil shells embedded in rocks along the side of roads headed east. Collectors have, over the years, picked up many of these easily collectible rocks. Now and then road cuts reveal new fossils. If you follow County Road 62 east into Weld County, the road cuts through Fox Hills sandstone, revealing oyster shells that once filtered their food from the waters of the seaway about 72 million years ago. Colorado law says even these road cuts are off limits for collection, while other states, like Kansas have no such statutes on their books.

Always ask permission from landowners (and know the laws for collecting on federal land) if you spot likely sites for rock, mineral and fossil collecting. It’s often easiest to join groups, like the Fort Collins Rockhounds (fortcollinsrockhounds.org) or WIPS (westernpaleo.org). Members of these long-standing clubs have contacts with landowners and/or experience hunting on government lands. They also know the most productive locations and the laws governing fossil collecting. For example, it’s often legal to collect invertebrate fossils on government land (in moderate quantities), but collecting sexier vertebrate material, like dinosaurs, fish, or brontotheres, could set you back with a fine or put you in jail.

With that in mind, here are a few places of interest, should the hobby of beachcombing the deep past appeal to you:

McCoy (population, 24): A 300-million-year-old Paleozoic site featuring crinoid (starfish relatives) and brachiopod (primitive clam-like organisms) fossils. Some public land adjacent to the town cemetery is accessible, but don’t wander onto nearby private property.

Ammonite nursery: Near the town of Kremmling is a site with giant (about 2-feet in diameter) fossil marine mollusks called ammonites. The BLM (Bureau of Land Management) conserves a protected site where you can see fossil casts and read about finds there. Hunting rocks and fossils is allowed on public land outside the protected area. The road into the area is rugged.

Kemmerer, Wyo.: Home to fossil fish that rest in huge sandstone deposits from three large lakes that dominated the area 55 million years ago. Visit Fossil Butte National Monument to learn about the area’s geological history. Warfield Fossils and other commercial sites allow digging for a fee. See www.FossilSafari.com for details about Warfield. Police will prosecute illegal diggers in this area.

Tepee Buttes: Various locations in El Paso and Pueblo counties in southeastern Colorado show these conical formations that are the remains of ancient methane seeps. Most are on private land, so membership in WIPS is the best way to explore these areas. WIPS member, Steven Veatch has more information here: http://coloradoearthscience.blogspot.com/2011/12/tepee-buttes-late-cretaceous-submarine.html

Comanche National Grassland: These grasslands stretch across southeast Colorado south of La Junta. Permits are required for fossil collecting. WIPS runs one or two trips a year in the area through permits acquired by a member who works closely with the state paleontologist. The grasslands are home to some famous Picketwire dinosaur trackways. The U.S. Forest Service does run some tours to the trackways for people with 4-wheel-drive vehicles.

If you want to see a few fossils, learn more about them, or even get one you’ve collected identified, mark Oct. 15 on your calendar. In celebration of National Fossil Day, I and several other WIPS members will be manning a table at the Fort Collins Museum of Discovery from 10 a.m. to 2 p.m.

Readers preferring to enjoy the wonders of the deep past in a more vicarious way may enjoy my graphic short story, “The Dinosaurs’ Last Seashore: or my SF novel “A Singular Prophecy.” Time-traveling paleontologists figure heavily in both. The titles are available directly from me or at Owl Canyon Coffee/North Forty News, 3745 Cleveland Ave. in Wellington.