A storm is expected to drop several inches of rain throughout the county, including areas recently burned by wildfires.
A portion of Highway 140 will close at 7 p.m. on Wednesday night.
In addition to the highway closure, all roads in Yosemite will close at 11:59 p.m. on Wednesday, park officials announced in a tweet.
All roads in Yosemite will close before 11:59 pm on January 16 due to a storm. Exceptions are roads within (but not to) Yosemite Valley, between Yosemite Valley and Foresta, and between South Entrance and Wawona. Call 209/372-0200 (then 1, 1) for updates.— Yosemite National Park (@YosemiteNPS) January 17, 2019
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With an already saturated mountainside and more rain ahead, Caltrans officials say they're not taking any chances.
"In this stretch, the Ferguson fire scar, the roadway is prone to mudslides. This gives us a chance to keep traveling public from road when mudslides are most likely," said Thomas Lawrence, public information officer for Caltrans.
A flash flood watch is in effect for several areas throughout the Central Valley, and the excessive rain could lead to mudslides along the Ferguson Fire burn scar.
The closure is about 17 miles, starting at Bear Creek near Midpines and ending in El Portal near the Yosemite Entrance.
"Our thought is to close the roadway, keep the public out. Better safe than sorry. We don't want anyone caught in that area if the mountain decides to come down," said Mariposa CHP Commander Richard Lindgren.
Snow plows and Caltrans crews are in the Merced River Canyon, and will be patrolling throughout the storm.
Both Caltrans and CHP officers were in the canyon on Wednesday making sure that anyone along the area leaves before the storm hits.
"There were four trucks yesterday and three overnight. There's going to be as many at five tonight, including some help from a Merced maintenance crews along with Mariposa and Midpines," Lawrence said.
The last time the highway closed was for storms in November last year.
That round of rain led to some mudslides near the burn scar.
The California Highway Patrol is helping Caltrans with the closure, but say all of Mariposa County will likely be impacted.
There's also a Winter Storm Watch for areas in Yosemite National Park above 7000 feet.
There's no estimated time of when the highway will reopen.
Officials say it's going to depend on if there's damage, and when crews determine the roadway is safe to reopen.
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