The Basics of Bisti/De-Na-Zin Geology
BLM says a little about the geology of the Wilderness, at http://www.blm.gov/nm/st/en/prog/wilderness/bisti.html
I am not going to discuss formations or geologic processes in detail, as I am no expert. These geology pages are based on information I picked up during a couple of hikes with BLM employees.
As you drive into the area of the Bisti/De-Na-Zin Wilderness, you can see that it exists in a sort of natural depression. Coming from any direction, you are on the short-grass prairie of the high desert (overgrazed and largely turned over now to sage, juniper and tumbleweed) and go downhill to the badlands that include the Wilderness. The surface of the prairie is sandy. If you start your trip in Farmington, you will see the high bluffs on the south side of the San Juan River. They are tan and the sandstone lacks sedimentary lines. This formation is the Ojo Alamo. The Fruitland Formation and Kirtland Shale, named after the towns that lie downstream from Farmington on the San Juan River, lie below the Ojo Alamo. They are the formations that are exposed in the Wilderness. As the BLM site says, generally the western, Bisti area, is Fruitland Formation, and the eastern, De-Na-Zin area, exposes the Kirtland Shale. These layers are characteristically rich in coal and fossils.
When you drive to the Bisti-De-Na-Zin Wilderness, you drive out of tawny sand and sage desert, into a world of gray, black, red and purple sands and rock (see photo above). The badlands do not support much plant life. Two BLM botanists told me on a hike in 2010 that there are eight species of plant that grow in the WIlderness. The Wilderness badlands result from the erosion of the sandy layers, leaving bare the thick deposit of volcanic ash that exists at the Kirtland/Fruitland layers in that area. The ash erodes very quickly and does not hold water long. These two qualities make for poor growing conditions.
The ash lies over the remains of a riverine delta. At the time these exposed layers were formed, the Wilderness was just to the west of the Western Interior Seaway* that covered much of New Mexico 70 million years ago. The fossils in the Wilderness mostly preserve a record of freshwater life on the edge of a great river delta at that time. Swamps and the occasional pond along that delta left behind large buildups of organic material. When you see a large pile of lignite (low-grade coal) sitting on the floor of the wash in Bisti today, you are looking at the remains of an ancient swamp or pond. These lignite beds coincide with most of the petrified wood and fossils you see on the badlands. Generally these organic remains are harder than lignite, so they weather out as the lignite erodes.
Much of the coal in Bisti burned in an ancient fire that I am told took thousands of years. The clay over the coal layer was metamorphosed by the heat into red "clinkers" that look today like tiny pottery sherds or perhaps chunks of brick, depending on size. They clink when you step on a concentrated cluster of chips - hence the name.
The ash, lignite and clinkers account for the characteristic gray, black, red and purple colors of the badlands. The purple is just a variation of the red clinker, for the most part.
On the De-Na-Zin (eastern) side of the WIlderness, the exposed layers coincide with the K/T boundary. It is one of the few pieces of public land in the world where you can see this. De-Na-Zin is less ashy and more sandy than Bisti, making for fewer hoodoos and higher hills.
*The Western Interior Seaway did extend as far west as the Wilderness at some point, depositing the Fort Lewis layer before receding to the east. Those sediments are not generally visible in the Wilderness today.
Click on the buttons above this overview, for more details on (i) the erosive nature of the landscape, (ii) clinkers and coal, and (iii) petrified wood and fossils. Other navigation buttons are at the very top of the page.
I am not going to discuss formations or geologic processes in detail, as I am no expert. These geology pages are based on information I picked up during a couple of hikes with BLM employees.
As you drive into the area of the Bisti/De-Na-Zin Wilderness, you can see that it exists in a sort of natural depression. Coming from any direction, you are on the short-grass prairie of the high desert (overgrazed and largely turned over now to sage, juniper and tumbleweed) and go downhill to the badlands that include the Wilderness. The surface of the prairie is sandy. If you start your trip in Farmington, you will see the high bluffs on the south side of the San Juan River. They are tan and the sandstone lacks sedimentary lines. This formation is the Ojo Alamo. The Fruitland Formation and Kirtland Shale, named after the towns that lie downstream from Farmington on the San Juan River, lie below the Ojo Alamo. They are the formations that are exposed in the Wilderness. As the BLM site says, generally the western, Bisti area, is Fruitland Formation, and the eastern, De-Na-Zin area, exposes the Kirtland Shale. These layers are characteristically rich in coal and fossils.
When you drive to the Bisti-De-Na-Zin Wilderness, you drive out of tawny sand and sage desert, into a world of gray, black, red and purple sands and rock (see photo above). The badlands do not support much plant life. Two BLM botanists told me on a hike in 2010 that there are eight species of plant that grow in the WIlderness. The Wilderness badlands result from the erosion of the sandy layers, leaving bare the thick deposit of volcanic ash that exists at the Kirtland/Fruitland layers in that area. The ash erodes very quickly and does not hold water long. These two qualities make for poor growing conditions.
The ash lies over the remains of a riverine delta. At the time these exposed layers were formed, the Wilderness was just to the west of the Western Interior Seaway* that covered much of New Mexico 70 million years ago. The fossils in the Wilderness mostly preserve a record of freshwater life on the edge of a great river delta at that time. Swamps and the occasional pond along that delta left behind large buildups of organic material. When you see a large pile of lignite (low-grade coal) sitting on the floor of the wash in Bisti today, you are looking at the remains of an ancient swamp or pond. These lignite beds coincide with most of the petrified wood and fossils you see on the badlands. Generally these organic remains are harder than lignite, so they weather out as the lignite erodes.
Much of the coal in Bisti burned in an ancient fire that I am told took thousands of years. The clay over the coal layer was metamorphosed by the heat into red "clinkers" that look today like tiny pottery sherds or perhaps chunks of brick, depending on size. They clink when you step on a concentrated cluster of chips - hence the name.
The ash, lignite and clinkers account for the characteristic gray, black, red and purple colors of the badlands. The purple is just a variation of the red clinker, for the most part.
On the De-Na-Zin (eastern) side of the WIlderness, the exposed layers coincide with the K/T boundary. It is one of the few pieces of public land in the world where you can see this. De-Na-Zin is less ashy and more sandy than Bisti, making for fewer hoodoos and higher hills.
*The Western Interior Seaway did extend as far west as the Wilderness at some point, depositing the Fort Lewis layer before receding to the east. Those sediments are not generally visible in the Wilderness today.
Click on the buttons above this overview, for more details on (i) the erosive nature of the landscape, (ii) clinkers and coal, and (iii) petrified wood and fossils. Other navigation buttons are at the very top of the page.