SAN FRANCISCO -- San Francisco's antiquated water main system gave way early Wednesday, triggering a geyser and flood that shut down the Mission District's busy Valencia Street before it could be shut off.

The break occurred at the intersection of 26th and Valencia streets at about 4 a.m., according to San Francisco Public Utilities Commission spokesman Tony Winnicker.

"This is an area where two major transmission mains cross," Winnicker said. "So it took some time to figure out which one burst."

Crews determined it was a break on an 80-year-old, 16-inch main on 26th Street. Once it was determined where the break was officials shut down that section of the main at about 7 a.m., he said.

Northbound Valencia Street reopened at 7:15 a.m. Southbound Valencia remains closed from 25th Street to Cesar Chavez. It will be closed until this afternoon, but it should be reopened for the evening commute, he said.

Water pressure that slowed down or stopped was restored to the area by about 7:15 a.m., according to Winnicker.

The exact cause of the break is unknown, but there tend to be more breaks during the winter, he said.