The Los Angeles Department of Public Works said L.A. Sanitation & Environment crews clean more than 38,000 catch basins and storm drains every year.
However, city officials tell Eyewitness News when it rains heavily in a short period of time, the storm drains can't handle the volume of debris flow and storm water runoff.
Michael Scaduto, a senior engineer with L.A. Sanitation & Environment, said the city's storm drains and catch basins are outdated and a lack of resources have prevented certain upgrades.
"What we've seen in the city is much of our storm drain infrastructure was built in the early 30s and 40s at a time when the city was not developed as heavily as it is now," he said. "We're pretty much a concrete jungle ... what that equates to is more runoff."
The storm dumped more than 11 inches of rain over three days at Mount Tamalpais, north of San Francisco.
More than 8 inches of rain fell in Santa Barbara County. More than 4.6 inches fell within 24 hours in Orange County's Silverado Canyon, south of L.A., unleashing mud that swamped some homes and led to damage and several rescues but no injuries.
Three cars washed down the concrete channel of the Los Angeles River when it became a raging torrent Tuesday. Two were pinned against a bridge abutment. No victims were immediately located and authorities had no updates Wednesday.
"Every time the road floods, it like totally inconveniences me to work and I'm only a couple of miles away," said resident Halina Lew. "So I always have to find the back way of getting there. Some money needs to go and get us a drainage system, or something, to cover the flooding situation that we have here."
Scaduto said the city has identified some of the larger projects it would like to focus on, but it won't be an overnight fix.
The Associated Press contributed to this report.