Timpanogos Cave, among the most popular attractions in northern Utah, is closing early this season so a long-stalled overhaul of the National Park Service’s visitor-staging area can begin along State Route 92 in American Fork Canyon.

The national monument’s last day of operation is Labor Day — Sept. 3 — after which work starts on relocating its visitor center, which has occupied a “temporary” structure in a rockfall-prone area since 1991. The National Park Service installed the current modular structure after its 1960s-vintage visitors center burned down.

“The interest was to use it for two or three years until they found the money,” said monument Superintendent Jim Ireland. “We have been in this trailer for 27 years, and it’s well past its lifespan.”

The project will also reconfigure the monument’s parking area in relation to the Alpine Loop Scenic Byway. The goal is to put all the parking on the south side of the road, reducing the need for monument visitors to cross it.

The monument typically closes for the season in mid-October, but crews will need to get started on demolition sooner to ensure completion in time for a summer reopening.

The $3.9 million project may be taking just a tiny bite out of the park services’s $11 billion maintenance backlog, Ireland said, but it will go a long way toward enhancing the efficiency of the attraction, which runs up to 510 visitors a day through its famous caves that were set aside as a national monument in 1922.

The new 1,900-square-foot visitor center is to be sited about 100 yards up the canyon from the current site, so it won’t sit directly under a cliff face that sheds rocks in the winter.

The project will not affect the 1.5-mile trail that climbs 1,100 feet to the cave entrance.

“But everything will be demolished around the trailhead,” Ireland said. “There will be no safe way to get to the trail during construction.”

Visiting the caves generally requires advance purchase of tickets. Most of the remaining tickets have already been sold, but the park service holds several each day for those who show up. The cost is $8 for adults, $6 for those age 15 and under.