The Bureau of Reclamation is currently working to secure a 500,000-pound slab of sandstone next to Glen Canyon Dam.

In the canyon walls of the Colorado River next to Glen Canyon Dam in Arizona, a massive rock slab threatens to fall.
According to the Bureau of Reclamation, the slab is "50-feet high, 30-feet wide and up to 4-feet thick." It weighs approximately 500,000 pounds. 
The risk from the slab was previously noted and rock bolts installed so that it could be more sufficiently secured and dealt within the days ahead.