Sierra National Forest

Current Conditions - Ferguson Rock Slide

CURRENT UPDATE

Current Rockslide Alert Level

NORMAL

Issued: Monday, February 9, 2009

In late fall 2008, the monitoring network for the Ferguson Rockslide underwent various activities.  This was to ensure the system would be functioning during the upcoming winter rains.  Global Positioning Satellite (GPS) stations A, B and C received upgraded circuitry from U.S. Geological survey personnel and related testing of the GPS and communications systems.  New batteries were also put in the units by Forest Service personnel. 
One of the water level monitoring stations on the Merced River was removed to facilitate installation of the new temporary bridges by CalTrans.  This station was re-installed with assistance from the California Department of Water Resources. 
The relatively dry rainy season to date has caused no significant change in the creep movement detected at the Ferguson Rockslide.  Current monitoring has shown a direct correlation of precipitation to movement of the Ferguson Rockslide.  When storm events result in 2 inches or more in rainfall within a 2 or 3 day period, the detected movement accelerates from 0.25 inches/day to 0.75 inches/day.  This acceleration decreases within days following the storm event.

Based on the level of movement measured at GPS stations A and B, the alert level remains at NORMAL. 

MONITORING PLAN

A monitoring plan was developed in order to provide information on the movement of the Ferguson Rock Slide. For more information on see the link below.

Monitoring plan >>>

AREA RESTRICTIONS

Vehicle length on Highway 140 is restricted to 45 feet in length. In the vicinity of the rock slide, traffic is diverted over two temporary bridges. Traffic is one-way and controlled by traffic signals. Expect short delays.

BACKGROUND INFORMATION

In April of 2006, a rock slide occurred in the Sierra National Forest, 6 miles west of Yosemite National Park more…..

ADDITIONAL INFORMATION

To view water height in the Merced River near each temporary bridge, go to the internet site for the California Data Exchange Center:

http://cdec.water.ca.gov/queryQuick.htm

Enter "FSU" for the station ID for the upstream station or “FSD” for the station ID for the downstream station.

To view geology reports on the Ferguson Rock Slide:

Ferguson Rockslide, USGS Open-File Report, June 23, 2006.

Simulations of Potential Runout and Deposition of the Ferguson Rockslide, Merced River Canyon, California, 2007. U.S. Geological Survey Scientific Investigations Report 2007-1275.