Tramonto and Castellammare area landslides
Location
Northbound State Route 1/Pacific Coast Highway (PCH) at Porto Marina Way, ¾-miles north of Sunset Boulevard, in Castellammare (the city of Los Angeles).
Current Work
Caltrans is leading an effort to restore PCH and monitor two landslides in the Castellammare area, which were first reported in 1936 and have created disruptions to traffic along PCH and damage to residences and city roadways along the hillside.
Work began in February 2026 to conduct an investigation into current conditions to ensure the safety of PCH from future storm and slide impacts. This work includes taking soil samples at nine locations, three on PCH and six on city streets including Castellammare Drive, Posetano Road, Stretto Way and Revello Drive. Caltrans is working with the city to secure permits for work on city streets.
Caltrans will use this data to create a Preliminary Geotechnical Report summarizing feasible alternatives to protect PCH from slide impacts and create a Final Geotechnical Report.
Background
The Castellammare Mesa area is home to at least two landslides that have been active since 1932 and moved slowly over the years. The slide area referred to as the “Tramonto Slide” is much larger than the portion visible on the highway. It is approximately three acres in size and has been moving intermittently since the 1930s.
The Tramonto Slide is a deep-seated rotational landslide. Rotational landslides occur along a curved or spoon-shaped surface. There is often a toe of displace material. Rotational slides often occur because the internal strength of the material is overcome by its own weight. They are usually composed of relatively loose or unconsolidated material. Water has a significant influence.
Deep-seated landslides are typically much larger than shallow landslides, are often slow moving, and can cover large areas.
FAQs
What work is happening now?
Caltrans will take soil samples at nine locations on Pacific Coast Highway, Castellammare Drive, Posetano Road, Stretto Way and Revello Drive. The department is working with the City of Los Angeles to acquire permits for all work on city streets. The nine locations are listed on the map below:
Crews will work at one city street location at a time, starting at location 7 on the map.
*Work on location 3 will not begin until city of Los Angeles completes reconstructing a retaining wall in this area, which is expected in April 2026.
**Caltrans drilled at locations 4, 8 and 1 on PCH at the end of February. It is currently working with the city to finalize a timeline for the remaining locations on city streets.
Will all nine locations need closures at one time?
No. Caltrans will work at one location at a time on the city streets. Work at each location is expected to last 1-2 days, depending on site conditions.
Drilling at the three PCH locations is complete.
What is the proposed schedule for this work?
The tentative schedule is fluid due to recent weather delays, utility clearances and ongoing construction by the city of Los Angeles near Posetano Road, which limits access to the site due to narrow street widths.
The proposed schedule for upcoming work is:
Feb. 28: Crews finished drilling at the three locations on PCH.
March 10-11: Prep work for drilling will start at one location at a time (roughly a few hours at each location) on city streets. Work hours are 7 a.m. to 4:30 p.m.
As early as March 17: City street work starts with drilling and soil sampling at location 7 on Revello Drive. This work is expected to take about up to two days, between 7 a.m. and 4:30 p.m.
The schedule for the remaining borings on city streets is still being finalized. After completing drilling and soil sampling at location 7, Caltrans plans to continue drilling at the remaining locations. Each site is expected to take about 2-3 days to complete.
What are construction hours?
On Pacific Coast Highway: 10 p.m. to 5 a.m. weekdays.
On city streets: 7 a.m. to 4:30 p.m. Mondays through Saturdays (only at one location at a time)
How will this impact traffic?
On city streets, Caltrans will reduce traffic to one lane at each location at a time while drilling occurs and provide traffic control during this operation.
Motorists and residents should expect traffic delays and noise associated with drilling during this work.
What permits has Caltrans received for this work?
City and county permits:
1. LA County Public Health Well Permit (SR0433335 for drilling soil borings approved 2/4/2026, currently application is being prepared/submitted to convert to monitoring wells).
2. City of Los Angeles Excavation Permit (E-Permit) (E-8500-0004, approved 1/15/2026)
Why is this work happening now?
This work is part of the Director’s Order emergency projects on Pacific Coast Highway from damages and impacts from the 2025 Palisades Fire and subsequent rainstorms.
I need the details. What is the full scope of work for the February 2026 investigation?
Field exploration will consist of seismic refraction surveys, boreholes with soil and rock sampling, and in some cases, downhole geophysical testing and/or installing instrumentation at all nine locations.
Caltrans will collect soil and rock samples, generally at five-foot intervals until material suitable for rock coring is encountered.
The site investigation will include field visits for planning purposes, utility clearance, drilling of six soil/rock borings on city streets of Revello Drive, Posetano Road, Stretto Way and Castellammare Drive. Following conclusion of the drilling, each borehole will have geotechnical monitoring instrumentation installed that will allow engineers and geologists to study the movement of the earth as well as the groundwater conditions over time.
Monitoring will be conducted at regular intervals through summer 2027, and the instrumentation will be removed by December 2027.
Boreholes not containing instrumentation will be backfilled with cement grout. Wells will be destroyed in according with Caltrans regulations and permit requirements.
Caltrans will reduce traffic to one lane at each location at a time while drilling occurs and provide traffic control during this operation.
The samples will be used to assess current conditions, analyze stability and identify possible ways to strengthen the slope and guide future safety improvements to protect PCH.
Slide activity
Spring 2025 to present
As part of its recovery efforts from the January 2025 Palisades Fire and subsequent rainstorms, Caltrans crews noticed impacts to PCH near Sunset Boulevard from the fire and rainstorms. They suspected the underlying causes of these impacts may have been previous landslide activity.
After clearing debris and restoring the state's damaged assets from the fire and storms, crews in February 2026 began working on a field investigation
February 2024 rainstorms
Slide activity that originated outside of state/Caltrans right of way was caused by a storm in early February 2024 and further saturated by additional storms in February and March 2024. The slide encroached onto Caltrans right of way, blocking the northbound right lane.
Because that slide was too unstable, Caltrans realigned lanes on PCH to create a second northbound lane. There was no additional space in the median to create another lane. All northbound and southbound lanes were shifted towards the shoreline to create space for a second northbound travel lane that allowed the safe and smooth flow of traffic.
Construction included removing the existing curb along the southbound shoulder; removing existing pavement delineation, markers, and markings; realigning lanes around the slide area; grinding; repaving; restriping; installing signs; and placing k-rail at the toe of the slide.
The additional northbound lane was opened to traffic the morning of Thursday, May 30, 2024.
Previous research
A joint study was done in 2010 by Caltrans and the City of Los Angeles, one of the property owners. The study documented the history of the slide and recommended that long-term repairs start from the top of the slide.
Research by the Caltrans Right of Way Division has determined that most of the property parcels in the slide’s land mass above the PCH are privately owned and some are owned by the city of Los Angeles. Once the slope has been stabilized from the top, Caltrans can continue with repairs at the bottom of the slide.
A permanent resolution to the Tramonto Slide area must be determined through communication with the owners of the property outside of Caltrans’ right of way. Long-term mitigation may require construction of infrastructure on private property, including multiple retaining walls. There is no estimate of when a mitigation plan will be established. Caltrans is communicating with the city of Los Angeles on the issue and both parties agree that a new study is required to determine the current status of the slide. A study will require securing and reviewing multiple core samples from the slide.
For more information or questions, email Katy Macek, Caltrans District 7 public information officer, at Katy.Macek@dot.ca.gov.