DEER VALLEY — The lifts are closed, skiers have all gone to their appointed evening destinations and, aside from a few scattered vehicles, the parking lots are empty.

That's when the real work begins. Drivers check tracks, oil levels and hydraulic systems, then start their diesel engines. Over the next 16 hours they will run their snowcats over as many ski runs as time and snow conditions will allow.

They will start on runs that are bumpy, grooved and chopped up, and leave behind runs that are smooth and very skiable.

Skiers, these days, expect to find the smooth runs. And, when they don't, "They let me know," said Chuck England, mountain operations manager for Deer Valley.

"The majority of skiers are at that level where they want groomed runs. For one thing, the snow is more predictable. Turns come more easily. Skiers feel better about their skiing when the runs are smooth. They also look better. At the end of the day people want to feel good about their skiing," he added.

All 13 Utah ski areas do some level of nightly grooming. In fact, few areas in the country don't groom.

"Sometimes we can't get to all of the runs. In some cases, when someone happens to ski one of those ungroomed runs, they let us know," said England.

"They'll tell me they're disappointed. They tell me that Deer Valley is known for its grooming and the run wasn't groomed. A lot of things come into play with grooming, like the weather and snow conditions, and there are times when we can't get as many runs groomed as we would like."

Grooming does require a major commitment on the part of the resort. Snowcats are not cheap. Also, as in the case of Deer Valley, it takes two full crews each working eight-hour shifts.

There are two companies that build snowcats — Prenots and Piston Bullys. Deer Valley has a fleet of 15 Prenots, two of which are wench cats. Each of the cats cost about $250,000.

Deer Valley started grooming runs even before it opened 1981.To introduce the resort, it hosted snowcat tours in 1979 and 1980. Many of its runs were groomed in order to give guests a good sampling of the mountains.

In the early days, basic snowcats pulled rollers, which were nothing more than large corrugated drainpipe about two feet in diameter. The rolling pipe did nothing more than compact the snow and flatten some of the bumps.

"The rollers were not very maneuverable and not very efficient. On steep slopes the rollers would often jackknife, so we were limited on the slopes we could groom," recalled England. New snowcats operate differently.