Cottonwood leaf in mud.
Cottonwoods lined the narrow road down Sheep Creek Canyon on the north side of the Uinta Mountains. Some were golden, some were bare. I assumed they were the narrowleaf cottonwood (Populus angustifolia), which is common in the Rocky Mountains, but when I looked close I found my old friend the lanceleaf cottonwood – same as the tree I’ve been following this year (Populus x acuminata).
Still fall in Sheep Creek Canyon ... but it's going fast.
Lanceleaf cottonwoods with 300-million-year-old sandstone in Sheep Creek Canyon Geological Area.
I met the second cottonwood species on the south side of the Uinta Range, at the old homestead of Josie Bassett. Josie staked a claim on the land in 1913 ... when she was 40, divorced, and with kids all gone. She built a house, developed the cattle operation, and ran it alone until shortly before she died at 90. The setting is spectacular. The house sits at the mouth of a box canyon in steeply-tilted and intricately-carved Navajo sandstone. Nearby I found the most beautiful cottonwood I’ve ever seen, in full autumn glory. It was a Fremont cottonwood, glowing in the morning light.
Deciduous trees at the mouth of the box canyon mark the Bassett ranch. Note golden cottonwood on right.
|Populus fremontii, part of explorer John C Fremont's botanical legacy.|
|Fremont cottonwood has distinctive broad leaves with coarse rounded teeth.|
My third cottonwood encounter was totally unexpected. Actually I didn’t see the trees, but their leaves were unmistakable. They lay perfectly preserved in 47-million-year-old mudstone of the Green River Formation (photo at top of post).
|The great lakes of mid-Eocene time. Lake Uinta was 270 across at maximum extent.|
Apparently cottonwoods also were common 47 million years ago, back when the Uinta Mountains were bordered by large shallow lakes. The climate was semi-tropical, perhaps like Florida's. For 15 million years, fine sediments and debris containing plant and animal remains were deposited on the lake bottoms. Now the sediments are rock – the Green River Formation – and the organisms are remarkably detailed fossils.
|State Fossil of Wyoming – Knightia. Source.|
I was well aware of the abundant fish fossils of the Green River Formation. They’re so common that one is the state fossil of Wyoming. But I didn’t know about the plant fossils until I entered the Eocene Gallery at the Utah Field House of Natural History State Park Museum in Vernal.
A wall covered in plant fossils!
The leaf display was astonishing. These leaves ended up on a lake bottom 47 million years ago, but they could just as well be last year’s, based on appearance.
|This leaf fell off a tree 47 million years ago!|
Fossilized sycamore leaf.
The scouring rush (Equisetum) below looks like our modern day ones. Note the tiny teeth on the dark bands – the free tips of fused leaves – and possibly the remains of a cone at the top. Below it is a modern-day scouring rush, also with a dark band of fused leaves, and a terminal strobilus (cone).
|Photo by Bruce Leander via the Lady Bird Johnson Wildflower Center.|
|Slab of Green River mudstone with leaf fossils.|
I was impressed by the the Field House. How many communities the size of Vernal (9100 people) have a museum of this quality? And why Vernal? Because it sits in the heart of the Dinosaur Triangle, with a fossil record that is "embarrassingly rich" (not just dinosaurs). But it's mission is broader. It includes interpreting the 80-mile radius around the town, including the Uinta Mountains. I took in all the exhibits, covering geologic history from Precambrian to present. They're modern, interesting, clear and justifiably enthusiastic ... if one takes time to read and look carefully. A booklet explaining the exhibits in more detail is available at the front desk (worth the extra $2.50).
|Stylinodon hangs out by a cottonwood tree on the shores of Lake Uinta.|
Bennis-Bottomley, MB. 2012. Fossil tales; an in-depth guide to the Utah Field House of Natural History exhibits. Utah State Parks and Recreation.
Sprinkel, DA, Park, B and Stevens, M. 2000. Geologic road guide to Sheep Creek Canyon Geological Area, northeastern Utah; in Anderson, PB and Sprinkel, DA, eds., Geologic road, trail and lake guides to Utah's parks and monuments. UGA Publ 29.