AILSA CHANG, HOST:
And I'm Ailsa Chang in Culver City, Calif., where yet another atmospheric river is dumping heavy rain and snow on the state. In the southern Sierra Nevada, local officials have issued evacuation orders for people living near the swollen Kern River.
ALLY SOPER: Water levels are exceptionally high, severe flooding.
CHANG: Ally Soper is chief communications officer for Kern County.
SOPER: A lot of these communities are rural, so likely these people have horses and other large animals that we need to ensure are brought to safety.
ARI SHAPIRO, HOST:
Outside coastal Santa Cruz, heavy rain is turning creeks into torrents. One local road collapsed overnight. Ashley Keehn of the Santa Cruz County Sheriff's Office says 700 people are stranded behind the washout.
ASHLEY KEEHN: Emergency access is cut off for the time being, but county crews are out there as we speak, working on a solution to get them emergency supplies and water and anything else that's needed.
CHANG: Heavy rains earlier this winter have already caused more than 700 landslides around the state. Geologists and engineers have been assessing that damage, and repair crews are working almost nonstop.
SHAPIRO: Amy Mayer reports from California's Highway 1, the iconic Pacific Coast Highway.
AMY MAYER, BYLINE: On a windy day, California Department of Transportation engineer Chris Risden is standing on a stretch of Highway 1 at Pescadero Beach, about 35 miles south of San Francisco.
CHRIS RISDEN: It's been around a long, long time, and it's been tricky.
MAYER: Highway 1 runs from Oregon to Mexico, clinging to cliffs and overlooking the ocean.
RISDEN: This was the first location that I was ever sent to to look at when I started here 22 1/2 years ago.
MAYER: He points to a brand-new guardrail that went in after January rains loosened a landslide and cracked the road. It's just one of many Caltrans' mitigations.
RISDEN: It's a very difficult sort of problem. There, we could just see a little rock just fell down. I don't know if you noticed that. A little rock...
MAYER: Yeah.
RISDEN: ...Is falling down the slope right now.
MAYER: When Risden identifies problems, he designs fixes to keep the roads safe. To keep up with constantly moving landslides, research geologist Jonathan Warrick creates 3D maps from aerial images. He's with the U.S. Geological Survey. He's walking on an abandoned road above Highway 1 in Big Sur. He carefully steps down into a jumble of broken asphalt and loose gravel.
JONATHAN WARRICK: Welcome to Paul's Slide.
MAYER: To the right, the shimmering Pacific; to the left, an active landslide. Below, bulldozers are creating a terrace to catch falling rocks, keeping them off the highway. Just to the south, he points to a roof that Caltrans built, turning a section of highway into a tunnel.
WARRICK: So that's a place where rocks continually rain down off that slope. And you can see on the roof - right? - all the rocks that are sitting on top of that roof.
MAYER: Instead of landing on the road or passing cars. Caltrans sometimes installs metal mesh right against the rock face to keep it from crumbling onto the road. Warrick's maps show how landslides are moving, but they can't predict when one will cause a problem. A steady soaking plus wildfires up the chances that trees and rocks will wash away. Warrick stops at another slide a few miles north that burned in 2020. That winter, rains flushed debris into a creek.
WARRICK: And it clogged the culvert running underneath the road and eventually eroded through the road. So we saw a complete failure of the highway here.
MAYER: Crews rebuilt the road with a bigger culvert, but in some places, Caltrans opts for a more dramatic solution. I'm currently on a trail that once was a section of Highway 1. In 1982 and '96 and 2006, Caltrans reinforced the ground and rebuilt the road. The community pushed for a more permanent change. Now the highway runs through a tunnel just inland from here, and this area is a park with beautiful ocean views.
GWENDOLYN HOLDEN: This is, like, the best place. I've seen so many things.
MAYER: That's local resident Gwendolyn Holden, who is here with her dog.
HOLDEN: It's easy for me to get to. It's easy for the dog. And then there's so much wildlife viewing.
MAYER: She's seen lots of whales and was hoping to catch the resident falcons today. Holden says the old, windy cliffside road felt harrowing at times. After a heavy rain, she still worries about rocks falling here.
HOLDEN: The big one right there - that does give me pause.
MAYER: Which is not Caltrans' goal, so crews continue to clean up rockslides in a constant struggle against winter storms. For NPR News, I'm Amy Mayer along California's Pacific Coast Highway. Transcript provided by NPR, Copyright NPR.
