March 2021

Columnar volcanic flows of andesite and basalt crop out as rimrock along SR-12 from Rim Rock Dam to the junction of SR-410 in Eastern Washington. One of the rimrock areas have been appropriately named The Royal Columns which consist of sub-vertical columnar joints formed in the volcanic flows of the Tieton Andesite above the Tieton River. This is popular area for rock climbing enthusiasts.

Because of the popularity of the area, Washington Department of Fish and Wildlife (WDFW) became concerned about an apparent unstable column of andesite that appeared to be separating from the main cliff when climbers reported a new tension fracture gradually opening to at least 2 inches between the hanging wall and the footwall in 2016. In April 2017 the rock column collapsed and destabilized adjacent rock columns. Fortunately, no climbers were injured and WDFW immediately closed the climbing area until the rockfall threat could be investigated.

WDFL asked McMillen Jacobs Associates (MJA) to investigate the recent rockfall. Most of the rock column had collapsed onto the bench and talus slope, however a residual rock wedge behind the original column of rock remained which posed a potential risk to climbers. MJA investigated the rockslope assisted by rope access techniques. The rock column appeared to initially have failed as a wedge and transitioned to direct toppling. MJA scaled approximately 3-CY of loose rock. After safety scaling was complete, MJA recommended the climbing area reopen for recreational use with the understanding, rockfall is an inherent risk.