It's nearly dark and somewhere, in the growing blackness, an animal is shrieking. I'm hanging from a tiny nub of volcanic rock 75 to 80 feet above the ground—just five feet away from the end of a long 5.9-grade climb—but I pause to glance over my shoulder at the mass of cows dotting Diablo Canyon's arroyo below me.

The shrieking grows louder. I don't move. I've heard stories about Diablo Canyon—they say that it's the devil's playground, that people see things there—and, in the fading light, scenarios start popping into my head, one after another, that make it impossible for me to move my aching fingers onto the next sliver of hard basalt.

My belayer yells up to me, "Erb, it's just cows! Get a move on it!"
"I'm from Iowa!" I yell back. "Cows don't sound like that!"

I laugh nervously and turn my attention back to the cliff. The distance between the end of the climb and my harness is defined by a taut, nearly horizontal 10.2 mm Mammut climbing rope. I'm even with the anchors but a good five feet to the right—and a fall here means I'd swing to the left, like a giant pendulum, and crash against a cheese-grater-like surface.

I take a breath. I'm on a top rope and this is an easy climb, but it's dark. This is the crux move and I can no longer see the tiny pockets, ledges and fractures that run throughout the cliff. My headlamp is in my backpack at the bottom of the climb. I start to move and reach up to a polished, slick hold. As I take a hold and step up, a chunk of rock breaks off beneath my slip-on climbing shoe. It moves silently at first and then starts to whizz, like a malfunctioning helicopter, as it gains speed toward my belayer's head.

"ROCK!" I shout.

It's late July and Rachel, my then-roommate, and I are having a full-on rock climbing love affair. We find reasons to sneak out of work early and she likes to wake me up on before 8 am Saturdays with a cup of coffee, a tentative smile and a "Come on, Erb. Let's go climbing already" after I've been out drinking at The Cowgirl and Del Charro the night before.

I'm not the nicest person in the morning. I stare instead of speaking and I let questions go unanswered. Rachel doesn't care, though. New Mexico is a diverse playground of jagged, soaring cliffs—iconic crags like El Rito, White Rock and the Enchanted Tower, among the lot—and she's itching to throw our rope bags into my busted-up Saturn and hit the road come dawn for another girls-only road trip. We go to crags, overpopulated with male climbers, and we put up routes without their help and guidance. I find it liberating. She finds it a good workout. We both find it normal.

The coffee hits my brain and soon I'm raging to go, too. The trip from Santa Fe to Diablo Canyon is a mere 30 minutes. The last 10 to 12 miles wind through desolate countryside—my sedan hums as it bounces along the pocketed dirt and across cattle grate after cattle grate.

The magnitude of the canyon hits me right as we enter the pebble-strewn parking lot. The arroyo that divides the two ridges is finally visible and the rocky hillside turns to cliffs that jut 300 feet upward from the wash. If you follow the sand, you'll wind up in the depths of White Rock Canyon and, later on, the Rio Grande. We stop short. Our two-pitch climb starts at the entrance, next to a broken-down fence post.

Diablo Canyon is home to more than 80 traditional and sport climbs, some 300 feet long. We hike to the top of a sharply inclined field of loose rocks and boulders, throw down our bags, shake out our ropes, slide into our harnesses and secure our helmets.

Here, a helmet is not optional. The rock is unstable. The extreme weather gradient that the canyon experiences shocks the rock and creates pressure points from within. Temperatures can swing from 0 degrees to 100 degrees in a single day. Footholds drop away without notice and belayers have to duck from the incoming bombs—a rock the size of a baseball can be deadly without a helmet.

Climbers started climbing in Diablo in the 1970s, jamming their feet, hands and gear in cracks to make it to safety. In the mid-'90s, sport climbers opened it up to a wider group by cleaning and bolting routes—screwing bolts into the side of the cliff so climbers could clip their ropes into these safe spots as they moved upward.

Rachel's my rope gun this summer. She's the fearless one, the better climber who's in charge of putting up the most difficult routes. I used to be a fearless lead climber until I banged my head against a wall during a climb two summers ago. Now I willingly give up the first climb to her. The pain of being upside down and smacking my head against the wall comes back to me as the rock I kicked loose careens toward her. I hold onto the wall more tightly, not knowing if my belayer is OK yet.

My shout, "ROCK!" echoes in the emptiness and I hear Rachel move closer to the cliff. Then there's a crack and a series of thuds as the rock picks up speed toward the sandy shores of the arroyo.

She curses like a fishwife before shouting, "I'm good!" It is her turn to laugh nervously.

I touch the top and she lowers me down. I lean back to stare at Diablo's desolate expanse. The cows have disappeared, the shrieking is gone, Rachel is OK, and as I slowly twirl back to the ground, I stare up at the stars lighting the sky above me.