Experimental helicopter water drops at Regents Slide were scheduled but ended up being during recent rains, which appears to have done something. The upper, dirt portion of the slide is moving on its own every day. I think some tens of thousands of yards came off over the weekend. 

Here’s a recent summary I sent to my institution a month ago.

Caltrans geotech has heavily-instrumented the upper portion of the slide due to its continuous movement. The movement has made it very hazardous to remove so equipment has been put on and pulled off the working bench repeatedly over the past few months. The attached photo shows the upper slide as of February 3rd, circumscribed in orange dashed lines. The original slide is on the back (south) side of a rocky, resistant ridge and well below this upper area. Debris from that rockslide can be seen 500 feet down on the highway on the right side of the photo. 

The plan has been to start above the rockslide section and cut it out using a working bench. The cut material gets pushed over the edge, gradually working downhill back to the highway. The upper slide section was destabilized by that process and started “rotating”, slipping downhill and outward, pushing over the resistant rocky ridge below. The arrows in the photo are my attempt to depict that rotation. The weight of the upper area to the left is causing the material to slide downhill but it is encountering the resistant material below. That is causing it to actually move horizontally and outwards to the right and to push out into the air, calving off like a glacier reaching the ocean or a lake. You can see there are two new slide sections at the horizontal arrows where the dirt is flaking off and falling down to the highway. 

Excavation is on hold while it rains. There is a presumption that as the soil gets heavier with water, the material will accelerate (not catastrophically fail) and reveal exactly where the slip plane is behind the slide. That will allow them to have a better defined plan moving forward. You can see their graded slope in the upper left of the photo. They need to keep that slope behind the slip plane as they work their way down to the right. 

Changes over the last month involve more dirt being pushed off the bench onto the slide (head) and the lower right (toe) calving off down to the highway. Also see attached two photos I took during the rain last week. Beneath the remaining vegetation there are fissures criss-crossing the moving section. It acts like a glacier, slipping off the top of the lower part of the larger slope, calving off the mountainside about 400′ above the highway. Impossible to put equipment on it when it’s wet.  They monitor it daily and pull off when it accelerates and jump back on when it slows down. 

That’s the latest from ground zero,
Mark

Here are the photos Mark references:

March 12, 2025 by Mark Readdie

March 14, 2025 by Mark Readdie

And from yesterday, March 18, which shows the recent drop:

Something I forgot to mention probably because I recycled a month old update. In addition to the two excavators and two other dozers, there are an additional two D8 dozers that have been retrofitted to wireless operation because Caltrans is pushing Papich to keep pushing dirt over the slip-plane crack but having an operator in the machines is too dangerous. The scale and complexity of this slide has pushed Caltrans into new technological territory in order to keep making progress. Perhaps a photo of all the equipment working on the slide would provide some scale. I’ll have to see if I can get that this week.