Simon Calder: The land of the free, now disfigured by barricades

The best decision of the day on Tuesday last week in Washington DC, when the federal government shut down? The bright idea of National Geographic to invite "all furloughed government employees and the general public" to visit its museum in the US capital free of charge.

Waiving the normal $11 (£7) admission provided the federal employees who had been sent home on unpaid leave something free to do. It also allowed foreign visitors the chance to look at some spectacular images of America's great outdoors – the only glimpse they are likely to get while the shutdown prevails.

The 800,000 workers tangled in the infantile bickering in the US Congress deserve sympathy – but so do the rather more numerous tourists who are directly affected by the shutdown. From the Cape Cod National Seashore in Massachusetts via Mount Rushmore to the Klondike Gold Rush historic site in Alaska, American icons have been cruelly put out of bounds.

When, in 1908, Theodore Roosevelt described the Grand Canyon as "the one great sight which every American must see," he could not have envisaged how planet Earth's spectacular wound would become a target for tourists from across the world. But, 105 years on, he would be appalled that thousands of international visitors are being turned back from the National Park gates while American politicians plumb the depths of absurdity. The UK equivalent would be for a row within the coalition about the NHS leading directly to the closure of Snowdonia, the Lake District, and all the best free museums in London.

As a result of Republican opposition to Barack Obama's health-care reforms, the National Park Service contingency plan swung into effect. Day visitors were barred from the Grand Canyon immediately, while guests staying at the park lodges and campgrounds had 48 hours to get out before park roads were closed.

The barricades went up to disfigure the land of the free. Staffing for a park that is the size of Norfolk (and scenically even more interesting) will be maintained "at the very minimum for the protection of life, property, and public health and safety".

By the time you get back to Phoenix you'll be furious – as are many local businesses, who are seeing their livelihoods, and the American reputation for a warm welcome, wrecked by Washington DC. At least Arizona offers much else to see, including some stunning State Parks that remain open.

But across in the great governmental theme park that is Washington DC, the main attractions are locked and barred because of the unseemly row on Capitol Hill. As The Washington Post succinctly put it: "If it's usually free, it's probably closed."

From the Freedom Trail in Boston to the San Francisco Bay, UK tourists find they are trapped in a nation on life-support, with not even the option of an escape to Alcatraz open to them.

We love America: its people, its history and its landscapes. But once again the tolerance of the British, who remain the most loyal of overseas visitors to the US, is being tested.