Caltrans: Topanga Canyon Boulevard slide remains active; top‑down grading and drainage planned, opening likely by fall

Caltrans officials told the Topanga Town Council on Thursday that the landslide that closed Topanga Canyon Boulevard is still active and will require significant engineering work before the road can be reopened.

Nina Choi, Caltrans Geotechnical Services chief, said geologists have documented ongoing movement and groundwater at the site and are watching for changes in vegetation, cracks and landmark movement. "The slide is still active," Choi said. She explained that what is visible from the roadway is only a small portion of the sliding mass and likened the condition to an iceberg, with much of the instability below the surface.

Caltrans has preliminarily estimated about 90,000 cubic yards of material would need to be removed—"akin to about 5,500 standard dump trucks"—and that the preferred mitigation strategy is grading from the top down once the slope dries enough for safe access. Choi said top‑down grading reduces the load that pushes the slide plane, and that drainage measures will be needed to address a natural spring and long‑running seepage.

The agency said it had considered but rejected some rapid‑removal options. "We don't want to blow it up," Choi said when asked about detonation, explaining that disturbing adjacent mapped earth flows could trigger larger failures. Caltrans also said tall retaining walls were not a preferred option for the scenic corridor because of size, anchoring demands and long construction timeframes.

Jim Medina, Caltrans public information officer, told residents the agency is "working aggressively to try to amend this situation" and that engineers are coordinating with State Parks and Caltrans environmental staff to secure permits before heavy equipment work can begin.

On timing, Caltrans provided a target of reopening by fall but cautioned that the date depends on slope stability, drainage work and environmental approvals. "We tentatively are looking at perhaps being able to open up the roadway by the fall," Choi said, adding that safety remains the top priority.

County and state officials on the call pledged continued coordination and to pursue options for expedited permitting and supplemental resources. Topanga residents pressed for faster fixes, second geotechnical opinions and clarification about whether disaster declarations or federal aid could accelerate work; state staff said the governor’s declaration and follow‑up federal approvals would be pursued to help businesses and explore funding options.

Caltrans said it will continue regular updates and that follow‑up meetings are planned so the agency can provide more technical detail and an evolving timeline.