From the Hall of Disjointed Memories, Part 35: A Monocline and a Grand Valley | Colorado National Monument, Colorado, USA
Snapped with my high-performance Kodak Instamatic along the lower portion of Rim Rock Drive 0.5 straight-line mi / 0.8 km southwest of the road’s junction with Route 340 (Broadway) in Fruita. I believe this means I was at the National Monument’s Historic Trails Viewpoint.
Facing northward.
The location cited above is based on the geometry of the Colorado River channel and on the location of the straight-as-an-arrow Broadway/Route 340 that runs from the town of Fruita across the river and into the National Monument. Out of the frame to the right is Grand Junction, the seat of Mesa County. It is there that the Gunnison River flows into the Colorado and boosts its flow considerably.
This was the first of two stops my geology-field-camp class made during our swing through this locale. It is a part of this glorious state remarkably different that the lofty peaks of the Front Range and San Juan Mountains. After all, we’d finally arrived in the Colorado Plateau physiographic province, a vast and uplifted land of often flat-lying sedimentary formations cut into spectacularly scenic buttes, mesas, and canyon walls by the Colorado River and its tributaries.
Geologically speaking, the three main stories here are:
- The Grand Valley that lies just to the north of the National Monument;
- Another dramatic exposure of the Great Unconformity discussed in Part 33, which will be featured again in the next post of this series; and
-The monoclinal nature of the bedrock in the park property itself.
In case you’re not familiar with the term, a monocline is a structural feature involving layers of sedimentary rock that have been compressed into a curious orientation. Whereas anticlines arch upward and then downward again, and synclines arch downward and then up, monoclines have beds that start by being flat at a lower level. They then angle upward and flatten out again at a higher level. There’s no arch shape at all. The whole thing looks something like two gigantic stair steps connected by a tilted riser.
In this photo, I’m still in the monocline’s lower portion. If I’m reading the map in the first source cited below currently, the sparsely vegetated rock surface just beyond the dead tree is 6the Jurassic-period Kayenta Formation sandstone. It’s a sequence of detrital beds laid down in braided streams in the Lower Jurassic. Notably resistant, it makes an excellent caprock, as we’ll see again in the next image, taken at a higher elevation at the crest of the monocline.
Every time I look at this shot I recall what I felt when I was actually here. I thought the valley was grand indeed, and I was impressed by how green and fertile it had become thanks to all the agricultural activity. Lush and verdant views are not common on the Colorado Plateau, but here human beings had once again made ample use of river-carved bottomland. Though I feel uncomfortable calling it that; the valley floor is some 4,500 ft / 1372 m above mean sea level.
Sources Consulted for This Essay
- Matthews, Vincent. Messages in Stone: Colorado’s Colorful Geology. 2nd ed. Denver: Colorado Geological Survey, 2009.
- Scott, Robert B., Anne E. Harding, William C. Hood, Rex D. Cole, Richard F. Livaccari, James B. Johnson, Ralph R. Shroba, and Robert P. Dickerson. Geologic Map of Colorado National Monument and Adjacent Areas, Mesa County, Colorado. Washington, DC: United States Geological Survey, 2001.
- Sebol, Lesley A., Katheryne H. McGee, Erinn P. Johnson, and P. E. Barkmann. Geology and Groundwater Resources of Mesa County, Colorado. Open File Report. Golden, CO: Colorado Geological Survey, 2017
You'll find the other photos and descriptions of this series in my From the Hall of Disjointed Memories album.
From the Hall of Disjointed Memories, Part 35: A Monocline and a Grand Valley | Colorado National Monument, Colorado, USA
Snapped with my high-performance Kodak Instamatic along the lower portion of Rim Rock Drive 0.5 straight-line mi / 0.8 km southwest of the road’s junction with Route 340 (Broadway) in Fruita. I believe this means I was at the National Monument’s Historic Trails Viewpoint.
Facing northward.
The location cited above is based on the geometry of the Colorado River channel and on the location of the straight-as-an-arrow Broadway/Route 340 that runs from the town of Fruita across the river and into the National Monument. Out of the frame to the right is Grand Junction, the seat of Mesa County. It is there that the Gunnison River flows into the Colorado and boosts its flow considerably.
This was the first of two stops my geology-field-camp class made during our swing through this locale. It is a part of this glorious state remarkably different that the lofty peaks of the Front Range and San Juan Mountains. After all, we’d finally arrived in the Colorado Plateau physiographic province, a vast and uplifted land of often flat-lying sedimentary formations cut into spectacularly scenic buttes, mesas, and canyon walls by the Colorado River and its tributaries.
Geologically speaking, the three main stories here are:
- The Grand Valley that lies just to the north of the National Monument;
- Another dramatic exposure of the Great Unconformity discussed in Part 33, which will be featured again in the next post of this series; and
-The monoclinal nature of the bedrock in the park property itself.
In case you’re not familiar with the term, a monocline is a structural feature involving layers of sedimentary rock that have been compressed into a curious orientation. Whereas anticlines arch upward and then downward again, and synclines arch downward and then up, monoclines have beds that start by being flat at a lower level. They then angle upward and flatten out again at a higher level. There’s no arch shape at all. The whole thing looks something like two gigantic stair steps connected by a tilted riser.
In this photo, I’m still in the monocline’s lower portion. If I’m reading the map in the first source cited below currently, the sparsely vegetated rock surface just beyond the dead tree is 6the Jurassic-period Kayenta Formation sandstone. It’s a sequence of detrital beds laid down in braided streams in the Lower Jurassic. Notably resistant, it makes an excellent caprock, as we’ll see again in the next image, taken at a higher elevation at the crest of the monocline.
Every time I look at this shot I recall what I felt when I was actually here. I thought the valley was grand indeed, and I was impressed by how green and fertile it had become thanks to all the agricultural activity. Lush and verdant views are not common on the Colorado Plateau, but here human beings had once again made ample use of river-carved bottomland. Though I feel uncomfortable calling it that; the valley floor is some 4,500 ft / 1372 m above mean sea level.
Sources Consulted for This Essay
- Matthews, Vincent. Messages in Stone: Colorado’s Colorful Geology. 2nd ed. Denver: Colorado Geological Survey, 2009.
- Scott, Robert B., Anne E. Harding, William C. Hood, Rex D. Cole, Richard F. Livaccari, James B. Johnson, Ralph R. Shroba, and Robert P. Dickerson. Geologic Map of Colorado National Monument and Adjacent Areas, Mesa County, Colorado. Washington, DC: United States Geological Survey, 2001.
- Sebol, Lesley A., Katheryne H. McGee, Erinn P. Johnson, and P. E. Barkmann. Geology and Groundwater Resources of Mesa County, Colorado. Open File Report. Golden, CO: Colorado Geological Survey, 2017
You'll find the other photos and descriptions of this series in my From the Hall of Disjointed Memories album.