This weekend, I had the opportunity to survey the damage from the recent storms in the Tejon Pass / Grapevine area. I took my motorcycle, as I expected to need extra clearance on some of the roadways I was going to take. The results of the survey were better than expected, mostly.
While I was only able to inspect the Ridge Route from State 138 south to the Tumble Inn, I was pleased to see how little damage was done to the roadway. As it has also been a while since I have been able to travel this section, I had to go by what I had heard and knew of the pre-existing damage. The bulk of the roadway was seemingly untouched by the recent storms. Only two sections, one with an existing problem, were a problem. One of those sections in particular, just south of Liebre Summit, is nearly impassable by a standard clearance automobile.
Mudslides, due to a locally heavy rainfall, closed Interstate 5 through this canyon for some time. Mudslide damage is still very apparent from near Ft Tejon north to near the lower escape ramp. Most of the slides affected the northbound lanes. These slides buried a significant section of former US 99 paving, especially between PM 5.5 and 6.0. While a more detailed inspection will be done later, it appeared that most of the exposed Ridge Route concrete along the northbound side was intact, with the later US 99 concrete being buried. The southbound lanes were also hit, though most of the old highway sections were still intact and relatively untouched.
Overall, the damage from these storms was very localized. As we approach a possibly strong El Nino winter, it is my hope that this storm was not a preview of things to come. As this winter progresses, this site will try to document the changes to our historic roadways throughout Southern California.
This weekend, I am travelling to the Liebre Mountains to inspect the damage from the recent storms on the Ridge Route, Grapevine Canyon, and the Ridge Route Alternate. I plan to inspect in detail those sections and take lots of photos. Updates on the status of the roadway will be initially via my Twitter account (@SocalRegionWeb) with a post update following. The sections I plan to cover in detail are Palomas Canyon (Five Mile Grade), Three Mile Grade, Ridge Route from State 138 to the Tumble Inn, Tejon Pass, and Grapevine Canyon. I’ll be taking my 2014 Kawasaki KLR 650 which will allow me access to more of the highway. Stay tuned for updates.
Southern California has many areas that are susceptible to landslides in many forms. The past couple of weeks have demonstrated that these slides can have dramatic affects on the regions infrastructure. While most slides aren’t that preventable, the damage they can create can be mitigated.
Understanding the signs of a pending landslide are fairly easy and should not be ignored. If you live in an area where landslides are possible, look for these signs:
- Ground cracks, particularly ones that appear to pull apart
- Sinking areas or changes in ground level
- Unexplained leaks in pipes
- Tilting poles
- New cracks appearing in a structure
- New springs or areas where water seems to drain without appearing on the surface
These signs are important to look out for. The first one, ground cracks, are the most obvious. They tend to arcuate and numerous. The largest ones may mark the head of the slide, though that is not a precise indicator of how large a slide may become. Ground cover itself doesn’t prevent deep seated landslides but it can help with smaller surficial slope failures. If you see any of these signs, please contact an engineering geologist or other local official to help assess the likelihood of a failure. Doing so can help prevent injury, loss of life, and property damage.
Mudslides, such as those that recently blocked Interstate 5 in Grapevine Canyon and State Route 58 in Cache Creek Canyon, are more common on steeper slopes with loose material. These tend to happen more commonly in areas which have burned recently, leaving little plant material and a soil that is less porous than it was previously. Those conditions, combined with a heavy rainfall, can turn that material into a thick mud which can easily move larger objects, such as boulders and trucks. As such, these slides can be very dangerous and fast moving.
The California Geological Survey has put together a series of maps to help determine the likelihood of a slope failure. These maps cover most of the metropolitan regions of California and are a great resource. They should, however, only be used as a guideline for potential slope failures. A more exact analysis should be determined through a geological report on your specific location.
Sometimes when a road gets realigned, a portion of the old roadway remains as an access road. This was the case when a small section of Rialto Ave (Arrow Highway/Route) was realigned in 1961 between Rancho Ave and Mt Vernon Ave. This realignment left behind a short span from the 1940’s. The bridge doesn’t have a date stamp nor is it still in the county bridge logs, so an exact date is tougher to find. Still, this bridge has a fine example of bridge rail from that era and is a good find.