Published Sep 18, 2026 9:52 am : Updated Sep 18, 2026 5:08 pm
Update at 5:05 p.m.: Highway 4 is back open this evening after a crash involving a big rig west of Mosquito Lake Thursday night. Hazmat cleanup efforts wrapped up just before 5 p.m., allowing the highway to reopen. Further details regarding the crash can be viewed below.
Original post written by BJ Hansen at 9:52 p.m.: Alpine County, CA—Cleanup is ongoing along Highway 4 in Alpine County due to a crash involving a big rig, west of Mosquito Lake.
The CHP reports that it happened at around 9:50 pm on Thursday. It involved a truck carrying isothiazolinone (synthetic preservative) that spilled into the dirt off the highway.
While traffic was able to get through for a while, the CHP reports that there is now a full closure to accommodate Haz Mat cleanup efforts. At this time, there is no estimate on when Highway 4 will reopen. Signs are up, starting in the Murphys area, alerting travelers to avoid the area. Vehicles arriving near the closure spot in Alpine County are forced to turn around.
This post was last modified on 09/18/2026 5:08 pm
Written by Tracey Petersen.
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