It was pouring as I drove my tin-can rental car up the hill outside Tucson.  This is crazy, I thought.  Crazy that it’s raining in the desert, and crazy that I haven’t turned back yet.

I listened to the news as I splashed along.  An 85-year-old man, known to have dementia, was missing: went to the supermarket, never returned home.

I pulled into the Tucson Mountain lot.  The rain suddenly stopped.  So I grabbed my knapsack and began to follow the first trail I saw.

A hundred yards from the car, I hesitated, confused.  The trail had disappeared.  Or rather, there were suddenly half a dozen trails: all formed in the past hour, by rivulets of rain.  Whatever footprints might have once marked the real trail had been washed away.  There was no one else around.

This must be what dementia feels like, I thought.

I turned around and spotted a stone shelter just above the parking lot.  My beacon: When I turned around, I would head straight for it.

I knew I was in no danger, not really, yet I felt queasy: do scorpions come out after a rain in the desert?  Rattlesnakes?  I had no idea.  Could the clouds gather again so quickly and rain hard enough to cause a flash flood?  Probably.

I felt small and humble and not very smart.  But I pressed on, thirsty for a little fresh air and exercise.  Twenty minutes, then I’d turn around.

40 minutes later, I made it back to where I started, dry and unbitten by any snakes (though I did have a cactus needle stuck in my sock), diving into the car just as it began to pour again.

Maybe it was the sheets of rain or maybe it was the fact that I didn’t have a Tucson map, but I got myself all turned around trying to find a café I remembered. I pulled into a 7-Eleven.  The cashier had no maps and didn’t know Tucson much better than I did.  But a girl in a pizza parlor shirt came in to buy cigarettes for her boss.  She looked so young the clerk carded her.  I asked her if she knew how to get to 4th Avenue.

“I just moved here from California,” she said.  “But I’ve got a map in my car.  You can have it.”

When I told my dad and stepmom I’d come down to see them in Phoenix, I did not expect rain.  I did not expect to get lost on a trail or in Tucson.  Visiting Phoenix, I am used to feeling like the youngster: invincible, unwrinkled (OK, maybe less wrinkled), high on Vitamin D.  Like the girl from California who no longer needed her map, not like the man I heard about on the radio.

After that first day, the sun came out and stayed out.  I took a map on my next hike, the beautiful Mormon Trail loop at South Mountain.

This time, there were plenty of footprints.  And other people, like the two men I passed—skin like armadillos, Lawrence of Arabia-style sunhats flapping—so deep in conversation they barely nodded at me.

“The thing about cosmology,” one said to the other, “is that it’s isotropic!”

      Isotropic: I looked it up later.  It means exhibiting properties—such as light transmission—that are the same in all directions.

The desert may feel isotropic after rain, but it’s not.  One way leads to confusion; the other back to the car.

We humans are not so isotropic either.  And yet.  If you pull out for the wide wide shot, we too are part of cosmology, of the infinite, isotropic universe.  Especially in middle age: we’re young, we’re old, we’re every age we ever were or will be all at once.  Sometimes in one hour of hiking.