Blacktail
Canyon (RM 120) is among the many scenic side canyons in Grand Canyon.
It is noted for its narrow slot and picturesque waterfalls in the
Tapeats Sandstone. Most visitors do not venture beyond the first
waterfall in the canyon. Several landslides and rockfalls in
the Bright Angel and Muav Formations are exposed in upper Blacktail
Canyon, a portion that must be accessed via a technical climb or by
hiking around the slot on its west side. The canyon widens dramatically
once it enters these weaker formations.
During
March-April 2005 we conducted a reconnaissance of Blacktail Canyon
(RM 120) while participating in a Grand Canyon River Guides training
trip. During the investigation, evidence of multiple landslide
dams and a recently formed rockfall dam were discovered.
Blacktail Canyon (RM 120) appears as a slot canyon in the Tapeats
Sandstone when viewed at river level.
Upper
Blacktail Canyon is littered with brecciated slide debris. These
landslides appear quite old and are highly eroded.
The above
picture shows a recent rockfall that has dammed Blacktail Canyon as
viewed from downstream (note person for scale). For now, the
course debris is allowing the intermittent flow of Blacktail Canyon
to run through the blockage and the dam has not breached.
Notice the ponding of fine-grained sediments behind the rockfall dam.
This occurs when the flowing water in Blacktail Canyon is temporarily
ponded behind the rockfall dam, allowing sediments to be deposited.
The sediments will likely one day plug the voids within the debris,
allowing it to retain water. Once this happens, the dam will
likely overtop and breach.
Several landslide dams have blocked Blacktail Canyon, forcing it to
divert around the blockages. The above pictures show an excellent
exposure of a buried channel within Blacktail Canyon on its east side.
These pictures were taken at the downstream end of the exposed channel
fill.
Questions or comments
on this page?
E-mail Dr. J David Rogers at rogersda@umr.edu
or
Conor Watkins at cwatkin@umr.edu.
