WHEN A. C. Thompson told me about his latest journalistic adventure – he wanted to go climb an 8,000-foot mountain in the middle of the desert to spy on a secret military base patrolled by security guards trained and authorized to use lethal force on trespassers – I said the same thing I seem to have to say at least once a month around here:

Jesus, Adam, don't get yourself killed.

And somehow, once again, he survived to tell the tale, this time of a UC Berkeley geographer who's fascinated by places that cover millions of acres of land – and aren't even on maps. Area 51, part of a sprawling Air Force compound in Nevada, officially doesn't exist. It's so clandestine that in the 1950s, the CIA encouraged rumors that there were alien spacecraft flying around the site, to distract people from the reality of high-altitude spy planes like the U-2.

The fascinating backdrop for this unusual travelogue is the fact that the "black budget" – the money the United States spends on projects so secret that even Congress doesn't know where the money is going – has risen dramatically in the past few years. And so has the level of secrecy. Twenty years ago, with the help of a young law student (now a lawyer) named Bill Simpich, I was able to figure out, fairly easily, some amazing information about the Reagan administration's secret plans for orbiting space-laser battle stations. All the space-policy and military wonks knew the outlines of the project (code-named TEAL RUBY), and we could find out enough from technical journals to piece it together.

Nowadays, even the wonks say they're utterly baffled by the money that's pouring into these secret bases. Could be just more spy planes. Could be weird and dangerous high-tech weapons. Could be some sort of war toys so outlandish that we can't even imagine them.

And you wonder who we're hiding all this from. The cold war is long over. Osama bin Laden has no use for, or interest in, spy planes. What war are we planning to fight with the $20 billion or so that's going for this stuff?

Or is it, maybe, that what they're building isn't even that important – but it's such a phenomenal waste of money (and such a great cash cow for a couple of military contractors) that they don't want the rest of us to find out?

Tim Redmond tredmond@sfbg.com