Gerda Stoof was delighted last week to be looking up at the 60-foot-tall stone faces of Mount Rushmore National Memorial near Keystone, South Dakota. She and her husband made a pit stop on their drive home from visiting new twin grandchildren in Ontario.
"I've heard about this all my life and have always wanted to see it," said Stoof, a native of Alberta, Canada. They were unaware that if they'd shown up a week later, the gates to the site of the iconic granite sculpture may have been locked.
That's because if Oct. 1 rolls around without the nation's lawmakers settling a budget for the new fiscal year, there may be a partial government shutdown that would affect the nation's more than 400 national parks and historic sites—including federal agencies that support tourism.
If there is a partial shutdown, it would cost the U.S. travel sector at least $185 million per day in lost economic output, U.S. Travel Association economists estimate. That could also lead to the loss of 530,000 travel-related jobs due to temporary layoffs, reduced wages and fewer hours worked.
"Entire communities will be affected beyond our national parks, because hotels, attractions, restaurants and retail stores will also lose revenue," said Roger Dow, USTA president and CEO. "The growing perception, and what could soon be a reality, is that the U.S. simply won't be open for business late next week."
In October 2013, when national parks closed for 16 days due to a budget stalemate, USTA calculated that travel spending was reduced by $680 million, or nearly $43 million per day.
The experience in South Dakota, where facilities at iconic Mount Rushmore were shuttered, was replicated at federally run sites across the country.
"Visitors informed our tourism bureau that they were canceling their trips," said Jim Hagen, South Dakota secretary of tourism. Tour buses were rerouted, while others turned around and left the state.
"That's hundreds and hundreds of hotel rooms that went unoccupied and thousands of meals that were uneaten," said Hagen, adding that key regions saw fewer jobs. "Hours were reduced and in some cases people were laid off."
Not everyone was a loser, however.
"We're a seasonal business and were already operating with a limited staff, but we benefited," said Brandi Hunsaker, manager of the Ruby House Restaurant in Keystone. The restaurant hosted busloads of tourists who had planned to have lunch at the national park site, but ended up in town instead.
"But I felt bad for the people who were maybe on a trip of a lifetime and couldn't see Mount Rushmore," said Hunsaker. "If it happens again this year, I think traffic will just dry up, we'll close earlier and it will cost us business."
In 2013, South Dakota was one of a handful of states where officials were forced to dip into their own coffers to reopen facilities closed by the national budget stalemate.
If there's a repeat of the government shutdown, Hagen said, the state is prepared to pay to keep Mount Rushmore open again.
"When you have people who have spent thousands of dollars, and in some cases tens of thousands of dollars to fly internationally, to come to your state, you want to do something to accommodate them," said Hagen.
"This year, we're having an incredibly strong fall shoulder season and we've had a very strong summer season. So another government shutdown could affect us in a major way," he added.
Lawmakers are making some progress toward avoiding a shutdown, but for now there's a notice posted on the Department of Interior website advising potential national park visitors to stand by. The agency is "in the process of reviewing and revising its Contingency Plans for Operations in the Absence of FY 2016 Appropriations," according to the department.
And just to be safe, tourism officials across the country—including in Washington, D.C.—are working on ways to get the message to tourists about all the attractions that will remain open, even if federal facilities temporarily close.
"We'd want to let the public know D.C. is open for business," said Elliott Ferguson, president and CEO of Destination, D.C., "Our city is home to a wide variety of museums, arts and cultural attractions, excellent dining, fine hotels and world-class shopping—the vast majority of which are open even in the face of a government shutdown."
—Harriet Baskas is the author of seven books, including "Hidden Treasures: What Museums Can't or Won't Show You," and the Stuck at the Airport blog. Follow her on Twitter at @hbaskas. Follow Road Warrior at @CNBCtravel.