LOS ANGELES—Heavy rain poured on the Southland overnight Dec. 29, prompting mudslides, debris flows, and flooding that made for a messy morning drive that was fortunately light due to the approaching holiday weekend. Snowfall forced the closure of Interstate 5 through the Grapevine early Thursday morning in northern Los Angeles County, while a mudslide blocked traffic and trapped some vehicles on Coldwater Canyon Avenue in Studio City, and flooding blocked the westbound Santa Monica (10) Freeway near the McClure Tunnel in Santa Monica. In Malibu, more than two dozen people had to be evacuated from Leo Carrillo State Beach campground due to flooding, which also led to closures on Pacific Coast Highway. Decker Road was closed at PCH due to multiple rockslides, according to the city, which also reported multiple instances of downed trees blocking roadways. A stretch of PCH was closed in Pacific Palisades due to a fallen tree …