DENVER (AP) _ It was the middle of the afternoon on one of the hottest days of the year when the air conditioners, refrigerators and elevators stopped working.

Stoplights went dark, stranding commuters in traffic jams. Long lines snaked out of gas stations. Stores had runs on ice, and office workers fled their sweltering glass-and-steel highrises.

``It takes no time to turn a modern office building into an incubator,'' said Mark Willoughby as he surveyed the traffic on Arapahoe Road, a major thoroughfare in busy southeast Denver. ``There's no ventilation and you can't open any windows.''

The problems did not last too long, from a half-hour to 1 1/2 hours. But they caused widespread concern, particularly in regards to elderly people without air conditioning and high-rise residents without elevator service.

Most hospitals and emergency services were not affected because they have auxiliary power plants. Air-traffic controllers switched to emergency measures as well.

At the 19-story Ambassador East condominiums in south-central Denver, the elevator didn't work and residents spent two hours stuck on the ground floor before the power came back on.

In Nevada, there were brief outages at casinos in Reno that went up on auxiliary power. Las Vegas was unaffected. About 90,000 customers lost power in northern Nevada.

In northern and central California, hundreds of thousands lost power. Carnival rides at Del Mar Fair outside San Diego suddenly shut down. Subway cars in the Bay Area Rapid Transit system stopped in their tracks.

The Los Angeles area water department shut down seven of its giant pumps for about an hour.

``There were outages everywhere,'' said Cameron Dalton, manager of First Interstate Bank in Oroville in northern California's Sierra foothills. ``The whole block was down.''

Businesses all over the West were affected. Some stores, bank offices, and restaurants closed for the duration. Others remained open, managing to make do without cash registers, computers, lights, refrigeration and other essentials.

One store, though, was prepared. At Vallerga's Market in Napa, Calif., one register continued to operate on a generator, allowing clerks to continue ringing up purchases.

``You can't get everybody through as fast, but we still speeded them through,'' clerk Christian Carvalho said.

Major banks that do business around the region, such as Bank of America and Wells Fargo, reported no major problems.

In Boise, Idaho, most offices and state agencies sent employees home and banks locked their doors during a two-hour outage. But sidewalk cafes in downtown Boise did a booming business.

Keith Kibe, manager of a Subway sandwich shop near downtown Denver, turned away customers looking for something cold to drink, using his ice instead to keep his cold meat from spoiling.

``We bought 60 pounds and it was going fast,'' Kibe said.