As much as 2,500 barrels (105,000 gallons) of crude oil, according to latest estimates, gushed onto San Refugio State Beach and into the Pacific west of Santa Barbara when an underground pipeline running parallel to a coastal highway there inexplicably burst on Tuesday morning.

Plains All American Pipeline, which owns and operates the line, said it shut off the flow about 30 minutes after control-room operators detected pressure irregularities.

By then, however, a torrent of oil had streamed down a canyon, under a culvert and out onto the once-pristine beach, blackening a 4-mile (6-km) stretch of sand and rocks and leaving two oil slicks in the water spanning more than 9 miles (14 km) in length.