Dozens of aftershocks rumbled through California's midsection today, one day after two powerful earthquakes left a couple hospitalized with serious skull injuries. Authorities warned jittery residents that more major quakes might be on the way.

A rescue team in a helicopter searched the rugged mountain terrain for anyone lost or stranded by Sunday's quakes.

Two shocks, registering 5.0 and 5.1 on the Richter Scale, rattled the resort areas of Mammoth Lakes and Yosemite National Park this morning, following Sunday's earthquakes, which were 10 times stronger and shook much of central California, sending boulders crashing down mountainsides. Nine people were reported injured, two seriously.

Carl Johnson of the U.S. Geological Survey said the aftershocks were rolling through the region "once every two or three minutes."

He said five field teams from the survey had gone to Mammoth Lakes, a community of 3,000 near the Nevada state line with instruments to gain more data on the tremors.

The area was spared major damage in Sunday's earthquakes, which were felt over most of California and as far away as Las Vegas. Numerous rockslides occurred, and some water lines were damaged but were quickly repaired, authorities said.

Mono County sheriff's deputy Randy desBaillets said today that authorities were advising hikers "to stay out of the immediate areas because of the possibility of rocks coming down from further tremors."