Florissant Fossil Beds, Colorado
Florissant Fossil Beds National Monument
is located in the mountains of central Colorado just west of Colorado Springs. It is
in a high valley sandwiched between the Pike's Peak massif and the hills ringing South Park. Grassy meadows alternate with
pine forests, and in July, the parks are ablaze with wildflowers: scarlet Indian paintbrush, blue-purple harebells, and every type of
yellow composite you can imagine. Add to this perfect temperatures and a crystalline blue sky, and you have the setting for a
delightful paleontological expedition.
We were working in the northwestern part of the park, assisting the National Park Service in attempting to relocate some
old quarries and excavate them for specimens to add to the museum's collection. The work was directed by Herb Meyer, the
park paleontologist, and Beth Simmons, a geologist who works at Florissant on the weekends. Herb had contacted the Western Interior Paleontological Society
to solicit volunteers, and that's how I got in on the dig.
The fossil-bearing layers are part of the Oligocene Florissant Formation, a volcanigenic unit about 34 million years old which
sits atop the Wall Mountain Tuff, a welded tuff capping the billion-year-old Pike's Peak Granite. The Florissant Formation consists
of several volcanically-derived units, some of which are lacustrine sediments and others of which are mud and debris flows. At
the time of its deposition, the Rocky Mountains had already been uplifted and a stream valley cut in the present location of the park.
A Sequoia-angiosperm forest growing in the area was covered by a mudflow that dammed the valley to the south when a
nearby volcano erupted. Some of the large
Sequoia trees were preserved in situ as standing trunks. A lake formed behind the dam,
and leaves and insects fell into the lake and were fossilized in the fine sediments. This sequence of events was repeated, resulting in
the deposition of some wonderful fossil-bearing layers. Although a few vertebrates and some snails have been found, it is the
plants and insects which have made Florissant famous and for which the national monument was established.
We had to walk about half a mile along an old jeep trail to reach the quarrying area. The sediments there are unbelievably fine,
and rock hammers are not appropriate tools. We found the most useful things to be small chisels (for prying), bricklayer's scrapers,
and palette knives. The shale disintegrated into cardboard-thin layers which had to be carefully removed from the hillside and
inspected for fossils. Many times a piece which appeared uniformly grey when fresh would yield compression-impression fossils of
beautiful leaves when it dried a little. Then we'd use a nippers mounted to a 1x6 to trim away the extra rock from around the fossil. If
the piece was very thin and fragile, Herb showed us how to use a little Elmer's to glue the playing-card-like piece to a heftier piece
of shale for a backing.
Most of what we uncovered were small leaves of angiosperms (flowering plants and trees), such as
Fagopsis, an extinct relative of the beech. There were also pine needles, white cedars, rose leaves, elms, one pine cone, and a bug or two. Although we didn't
of course find them all, over a hundred types of leaves are known from the formation, including oaks, willows, sycamores,
ferns, horsetails, sassafras, mulberry, walnut, birch, hawthorn, apple, maple, sumac, and many others, some representing
completely extinct groups. Most of the specimens were very well preserved by the fine sediments and showed the details of leaf venation
upon examination with a hand lens. Herb told us that the pattern of leaf veins was very important in diagnosing the taxon to which a
leaf belonged. Some two hundred types of bugs, from flies to butterflies to spiders, also come from the same sediments, but
they seemed to be hiding while we were there. We carefully wrapped all of the specimens Herb wanted to keep in toilet paper and
placed them in pop flats before loading them in the truck at the end of the day.
My mom and I were only there for one weekend, although Herb had volunteers helping during weekends throughout July. Being
a national monument, all specimens are government property, so we couldn't keep any of the fossils that Herb didn't want. But right
outside the park is a privately operated quarry, Claire Ranch, where you can dig through shales of the same formation for a small fee
and keep what you find. We went back there with my five-year-old daughter, Allison, late in September, and she found the best leaf
of all: both halves of a four-inch specimen of the hickory
Carya libbeyi. We had great fun, both digging for the park service and at
the private quarry. And you can't beat the scenery!
Check out another paleobotanical excursion to Sailor Flat, California
