Arizona's border guards and the law
We've just driven through Tombstone, the town famous for one of the most notorious shoot-outs in the Wild West, the gunfight in the OK Corral.
The dusty streets and wooden buildings recall a time long past. But Arizona is gripped with the fear that this beautiful big country is returning to a state of lawlessness, where the bad guys and their guns threaten the law-abiding.
More on the reality behind that fear later in the week (I had suggested it would come today. Apologies: it's a matter of co-ordinating various BBC outlets).
There's been a lot of debate about how the proposed new Arizona immigration law will affect American citizens and foreigners who are here in the United States legally.
We were about to find out.
A few miles outside Tombstone, all traffic was diverted into a makeshift checkpoint across the highway, about 25 miles north of the Mexican border. The border patrol guard asked if we were American citizens. My producer Regan Morris is, and he accepted her word for this.
Camerawoman Maxine Collins and I replied that we were British. Maxine made to hand over her driving licence, which is accepted as ID by police and at airports. He said this wasn't good enough and asked to see our passports and the residence visas inside them.
"You'll be OK if you are carrying these," he said.
We were, and we were on our way.
Does this bother me? Not personally. I nearly always carry my passport, and always when I am working. I knew when I lived in Belgium that by law I always had to have my commune (council) ID or passport on me. No problem. But no-one has ever remotely suggested I must do this in the States.
So the border guard's action does raise questions about the proposed Arizona law and suggests that it just extends to the police what the border guards are already doing. For that, some will feel safer, but others harassed.
Immigration lawyers say US law requires foreign visitors to carry an "alien registration" document - but not a passport and visa. But I don't know of any foreign national who's aware of this requirement - and I certainly wasn't.
And it's worth noting that in Judge Susan Bolton's decision last week throwing out the most controversial parts of Arizona's new immigration law, she cited the federal government's thinking on the matter.
"The federal government has long rejected a system by which aliens' papers are routinely demanded and checked," she wrote.