MOAB, Utah—Southeast Utah is among the most popular tourist destinations in the U.S. with two national parks and millions of undeveloped acres.

But visitors are increasingly spending more time sitting in their cars as they wait to access the vast outdoors.

“Anywhere you go, there’s going to be a line,” said Libby Preslock, who on a recent Thursday arrived at Arches National Park at 9 a.m. only to find that it was full and signs encouraged visitors to come back in three to five hours. She then headed to the area’s other national park, Canyonlands, where she waited about half an hour to get inside.

With its natural stone arches, sandstone fins and towering red rock formations, Arches attracted about 194,000 people in April, up 15% from April 2019. It was closed in April 2020 due to the pandemic.

Arches reaches capacity and closes its gate to visitors most days before 9 a.m., according to the park social-media channels, which send out real-time tweets when the park temporarily closes because its parking lots are full. Those who can’t get in often head to Canyonlands, a traditionally less popular park more than four times the size of Arches. Canyonlands has seen its own visits jump 30% in April 2021 from April 2019, to nearly 117,000. Lines to enter Canyonlands can stretch up to two hours during peak visitation times.

Lines to enter Canyonlands in Utah can stretch up to two hours during peak visitation times.

Lines to enter Canyonlands in Utah can stretch up to two hours during peak visitation times.

Nearby lands controlled by the Bureau of Land Management have seen an increase in visitors, particularly among first timers, says Nicollee Gaddis-Wyatt, field manager in Moab. A growing number of them are getting stuck while driving on dirt roads.

Last week, a wildfire began to spread less than 20 miles south of Moab after officials said a human-created campfire was left unattended. The blaze originated in a day-use area in the U.S. Forest Service lands and had burned more than 5,100 acres by Saturday morning. Two campgrounds and a residential community were evacuated.

Arches and Canyonlands have fewer than 100 designated campsites between them, and visitors are increasingly camping out on nearby federal land, some of which isn’t intended for tourism or overnight stays.

“People could be parked right next to a sign that says ‘closed to camping’ and they’re just like, ‘But the app said it was open,’” said Ms. Gaddis-Wyatt.

The boom in visits to national and state parks—largely attributed to a widespread desire to leave home as the pandemic eases—began when most reopened last summer.

But the surge of tourism is now reaching new heights. Dead Horse Point State Park, near Arches and Canyonlands, saw twice as many visitors in March 2021 as it did in March 2019. Wyoming’s Buffalo Bill State Park saw a 37% increase in visitors last year compared with 2019, which officials said is due in part to people stopping in on their way to Yellowstone National Park, located about 40 miles away. Yellowstone saw a 50% increase in vehicle entries over Memorial Day weekend this year compared with the same weekend in 2019.

The jump is boosting economies in places like Moab, where surrounding Grand County recently reported the highest sales and use tax revenue ever in the third and fourth quarters of a year, said Chris Baird, county administrator. Businesses are so desperate for workers that a Moab McDonald’s has a sign offering $18 an hour, more than double the state’s minimum wage. A spokesman for McDonald’s declined to comment.

Many residents say they are increasingly frustrated, as graffiti and piles of human waste are appearing where people are camping far from toilets, trash cans and any law enforcement. In addition, more visitors are parking illegally, walking along roadways not intended for pedestrians, and spilling off designated trails and damaging fragile soil crust, according to park officials.

Arches and Canyonlands have fewer than 100 designated campsites between them. Areas controlled by the Bureau of Land Management have seen an increase in visitors.

Arches and Canyonlands have fewer than 100 designated campsites between them. Areas controlled by the Bureau of Land Management have seen an increase in visitors.

Some tourists say their visits are less enjoyable, as they spend their days in hourslong lines and, when they finally get to popular attractions like the free-standing Delicate Arch in Arches, are surrounded by Disneyland-caliber crowds. “Out of the five national parks, this is probably one of the most unique, but I definitely wouldn’t say it’s my favorite because there’s too many people,” said Susan Mathews, who traveled to Utah’s national parks with her husband from Texas.

Funding for the national parks hasn’t increased in proportion to visitation. Between 2011 and 2019, the National Park Service lost 16% of its staffing capacity while at the same time witnessing a 17% increase in visitation. Between 2010 and 2019, Arches lost 7% of its base full-time staff, but was able to make up for those losses based on revenue from fees, according to John Garder, senior director of budget and appropriations with the National Parks Conservation Association, a nonpartisan organization that advocates on behalf of the national park system. Canyonlands lost 20% of its base full-time staff during that time.

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The Biden administration has proposed an increase in funding for U.S. national parks in its budget for next year, which Mr. Garder said would allow the agency to return more than 1,000 staff positions across the park system.

A spokeswoman for the National Park Service declined to comment on staffing levels.

The problem is exacerbated by the booming real-estate market, as many rangers can’t find a home in Moab and the next closest town is 50 miles away. Moab saw an increase in remote workers during the pandemic, and is a popular market for people buying second homes. There is currently about one week’s inventory available, says Dave Bierschied, owner of Moab Realty.

Several current initiatives aim to help educate visitors, including a campaign from the National Park Service to “plan like a park ranger,” advising guests to plan ahead and stay distant from wildlife.

To better manage the crowds, some residents and park advocates are pushing for Arches to institute reservations similar to those in place this year at Rocky Mountain National Park in Colorado, Yosemite National Park in California and Acadia National Park in Maine. They allow people to book windows to enter the park.

Canyonlands has seen its visits jump 30% in April 2021 from April 2019.

Canyonlands has seen its visits jump 30% in April 2021 from April 2019.

But local business owners have argued against it. Kent Green, owner of Moab Cowboy Country Offroad Adventures, said the system would deter visitors from traveling to Moab, particularly those planning last-minute trips, who he said could skip over town if they worry they can’t get into the parks. “I think it will kill our economy,” he said.

The park service said all options are on the table, and it plans to meet with the community later this summer to discuss long-term solutions to the crowding. Vanessa Lacayo, a public-affairs specialist at the National Park Service, said, “I think our goal is looking at broadening access, but doing so in a way that makes sense for long-term use.”

Canyonlands in May.

Canyonlands in May.