Hilary, the first tropical storm to move into Southern California since 1997, marked the first time ever that tropical storm watches were issued in the region.

Sunday set a new record for the wettest August day ever in Palm Springs, San Diego and downtown Los Angeles.

Hilary's highest rain total was in Upper Mission Creek in San Bernardino County, where 13 inches of rainfall was recorded.

-ABC News' Melissa Griffin

In Forest Falls, California, about 700 people are sheltering in place after mud and debris flow cut a road off from the rest of the community, according to the San Bernardino County Fire Department. No injuries were reported and crews are working to restore road access, the fire department said.

In nearby Seven Oaks, another 30 people are sheltering in place after flash floods struck several cabins in the area, the fire department said. Crews are working to access the residents and evacuate them, the department said.

All tropical storm warnings have been canceled across Southern California as the remnants of Hilary, which no longer meet the threshold of a tropical cyclone, track north, according to Ariel Cohen, meteorologist in charge at the National Weather Service Los Angeles.

Residual mudslides and rockslides are still a threat in California from the weekend rain.

The moisture from Hilary is now moving through the Rockies. On Monday, the flooding threat will be from the Sierra Nevada mountains into the northern Rockies in Idaho and eastern Oregon.

Los Angeles "avoided a potentially catastrophic set of conditions" from Hilary, LAUSD Superintendent Alberto Carvalho said Monday.

Carvalho defended the decision to close LA's public schools on Monday citing reasons including that many students walk to school and many employees live outside of LA.

"It would have been reckless for us to make a different decision" on Sunday, he said.

Schools appear to be in good condition, he said, noting that about 24 schools don't have phone or internet access and one elementary school that serves students with disabilities appears to have been impacted by a mudslide.

Carvalho said students should expect to resume their regular school day on Tuesday.

The National Oceanic and Atmospheric Administration's Weather Prediction Center issued a rare "high risk" forecast for excessive rainfall for Sunday across a large swath of Southern California, from Palm Springs up toward Death Valley.

"High risk" forecasts are only issued a couple times a year on average, and 39% of all flood-related fatalities and 83% of all flood-related damages in the U.S. occur on those days.

A "moderate risk" for extreme rainfall has also been issued from Las Vegas to San Diego and Los Angeles. Numerous flash floods could unfold in these areas as well, with some of them potentially significant and very dangerous.

The deadliest hazard associated with tropical cyclones over the past decade is flooding from heavy rain.

-ABC News' Dan Peck