Valencia Street between 25th and 26th streets reopened at about 1 p.m., San Francisco fire Lt. Ken Smith said.
The cause of the blaze, which burned buildings at 1470 Valencia St. and 1476 Valencia St., has not yet been determined, however Smith said investigators have the information they need and will be compiling notes and evidence to determine its origin.
The fire does not appear to be suspicious.
Those displaced by the blaze were able to return to their units at about 10:30 a.m. to collect some of their belongings, Smith said. "The residents, I think, will be surprised when they go in by the great work firefighters did," Smith said earlier today.
He said about 80 percent to 90 percent of the units received water damage and were "thrashed a bit," but were not burned.
Both buildings are uninhabitable and are going to have to undergo extensive repair, Smith said. The buildings have been turned over to there owners.
The Salvation Army is serving meals to displaced residents at the Mission Recreation Center, which is acting as an American Red Cross shelter. The Salvation Army is planning to serve meals through Wednesday, when officials will reevaluate the need.
Red Cross spokeswoman Melanie Sanders said the shelter was set up Monday night and about 21 residents displaced by the fire stayed overnight at the shelter. Caseworkers were working with the displaced this afternoon to help find possible alternative housing, said Sanders.
The blaze, which forced a temporary evacuation of the entire block, was first reported at 5:56 p.m. Monday, according to Lt. Mindy Talmadge. When fire units arrived on scene they found the rear of both buildings engulfed in flames, as well as the attic.
One reason the fire was so difficult to fight is the shape of the buildings, Talmadge said. The four-story buildings are very long, about 60 to 80 feet, which meant that when the fire reached the attic it could spread along the entire length of the structure.
The fires were burning on the fourth floors of both buildings and pushing against each other, allowing flames from each building to feed each other, Smith said.
Flames began to lick at the structure at 1488 Valencia St., Talmadge said, however firefighters were able to "put a wall of water" between the fire and the building and it was saved from any damage.
The fire was controlled at about 7:35 p.m. and fire crews monitored the buildings throughout the night.
Residents of 1488 Valencia St. were able to return to the building at about 9:30 p.m., said Smith.
There were no major injuries inflicted by the fire, however one firefighter and one resident were treated for smoke inhalation, Talmadge said.
Four pets were killed in the blaze and there were four pet rescues, said Smith.
