Still, the mandatory evacuation order remained in place Monday for Butte, Sutter and Yuba counties.
The evacuation was ordered Sunday after a massive hole was discovered in an emergency spillway -- which catches excess water when Lake Oroville's water level rises to overflow the dam -- threatening communities downstream.
Some people had just a few minutes to prepare to evacuate, in what one Oroville resident described as "pure chaos."
Stores closed. Shelters opened. Police manned roadblocks. Evacuees waited in traffic trying to escape low-lying areas. Residents mobbed gas stations on their way out of town. By early Monday, many of the pumps at those gas stations had yellow tape across them, indicating they were out of gas. Downtown Oroville was empty.
Butte County Sheriff Kony Honea defended the decision to evacuate, saying the "dynamic" situation required a quick response.
"We did this because our primary purpose is to ensure public safety," he said in a Monday news conference.
Gov. Jerry Brown praised the cooperation between local and state and civil authorities. In a news conference Monday night he said he spoke with a member of President Donald Trump's cabinet to request federal response aid.
He defended California's flood infrastructure and said he welcomed "more scrutiny" as mitigation efforts continue.
"Things can fail whether it's levees or dams or bridges," he said. "We're doing everything we can to get this dam in shape so [evacuees] can return and live safely without fear."
Situation improving at the dam
The Oroville Dam provides flood control for the region. The dam has two spillways to release water out of the lake to prevent overflow. Both have problems.
In the main spillway, which is lined, or paved, erosion has caused a hole almost the size of a football field and at least 40 feet deep to form in the lower part of the channel. It can't be fixed immediately.
The emergency spillway, which is an embankment covered with trees, is a last resort and was used for the first time in history on Saturday when the lake topped 901 feet, its capacity, and a light flow of water washed into the spillway.
Crews worked Monday to restore water levels and to repair dam controls before rains expected later in the week.
Water is no longer flowing over the emergency spillway and lake levels are continuing to fall, Honea said. The goal is to lower lake levels by 50 feet in anticipation of the rain, which could come as soon as Wednesday.
These efforts come amid mounting questions about why more had not been done to prevent spillway erosion after concerns were raised more than 10 years ago
. California Department of Water Resources Acting Director Bill Croyle said he was "not familiar with 2005 documentation
or conversation" about spillway concerns and emphasized the efforts underway to understand the current dynamics of the dam.
"We're going to continue to work on the challenges we have," he said.
Officials warned Sunday that a 30-foot "wall of water" could be sent rushing downstream if the eroding spillway were to collapse.
Honea's office issued a dire warning on social media: "This is NOT a drill." Officials said the spillway was in danger of failing any minute.
"Everyone was running around," Oroville resident Maggie Cabral told CNN affiliate KFSN. "All of the streets were immediately packed with cars, people in my neighborhood grabbing what they could and running out the door and leaving."
RaeLynn Jones said she received a notification on her phone around 4:15 p.m. followed by a text message from her father saying she had 30 minutes to leave before waters would flood her Oroville apartment near Feather River. She and her fiance grabbed as much clothing as they could each fit in a bag along with toiletries and electronics. Less than 30 minutes later they had packed up their car and hit the road with their dog, heading for her fiance's home, which is on higher ground.
"It was pretty stressful to move everything we could in 25 minutes," she said.
When they returned to her apartment Monday to pick up more items, her building was unscathed, Jones said. So was downtown Oroville. At Feather River, however, where the water level nearly reached the treetops, the water's force was evident. Surrounding playgrounds, gazebos and sports fields were completely submerged, she said.
Nine people and three dogs are now sharing her fiance's home in Foothills where she's riding out the evacuation order. For now, all they can do is wait.
"I'm a little concerned because I've heard about all the pressure pushing up against the emergency spillway, especially with rain coming."
Racing Wednesday's rain
The Sacramento Fire Department echoed the urgency and warned residents that the spillway failure could have effects, including flash flooding, 75 miles downstream in Sacramento.
Sean Dennis, who lives 30 miles south of Oroville, spoke to CNN from his car after spending 4½ hours in heavy traffic.
"It was pretty scary, just because of how fast everything was developing," he said. "Me and my wife managed to throw as much stuff as we could into garbage bags, whatever we could find. We got both of our cars loaded down pretty well. We're not taking any chances."
After issuing the evacuation orders, authorities noted significant decreases in the water coming over the emergency spillway. The urgency later subsided, with authorities reporting that the situation was not as desperate as previously thought.
Still, Honea said Monday he wasn't taking any chances by prematurely lifting the evacuation order.
"It was a hard decision to make but I can tell you the decision to release the evacuation is an equally difficult decision."
The main spillway was releasing water at 100,000 cubic feet per second Monday afternoon in an effort to reduce the amount of water traveling down the emergency spillway, Croyle said. Normal flows down the main spillway are about 55,000 cubic feet per second.
Crews used helicopters to drop bags of rocks into the gouged portion of the emergency spillway, in an effort to plug the hole.
"When or how long this takes depend on the dynamics of watershed," Croyle said Monday.
Unprepared after years of drought
Oroville Dam is the country's tallest. The emergency spillway that's eroding had never been used before in 48 years of existence, the DWR said. The closest it came to being used was in January 1997, when Lake Oroville's water level rose to within a foot of flowing over it.
The area had long been in drought, until this year, when heavy rain and snow bombarded the state. In Oroville, the average annual rainfall is about 31 inches, but since October, the Feather River, which begins at Lake Oroville, had already seen 25 inches of rain as of Saturday, according to the California Department of Water Resources.
The lake also gets water from the northern Sierra Nevada mountain range, which is experiencing one of its wettest seasons.