There’s a book called Over the Edge: Death in the Grand Canyon. The cover depicts a human skeleton lying at the canyon rim, not subtly. It’s not so much a safety manual as a collection of terrifying stories—it promises “gripping accounts of all known fatal mishaps” in the canyon.

The author at the edge of the North Rim the evening before the run (Sarah Yager / The Atlantic)

Most of them involve falling. I don’t have the book in front of me, but I imagine it starts with something foreboding, like “Nobody plans to fall into the Grand Canyon ...”

Yet people do. A “newly expanded” tenth-anniversary edition of Over the Edge came out in 2012, and even that is no longer a comprehensive catalog. Last year a 35-year-old Florida woman made news when she fell 400 feet over the edge to her death—shortly after posting what would be her final Instagram, a photo of her sitting at the edge.

I came across the book as I was preparing to run across the Grand Canyon. This would require going over the edge—down from the North Rim, across the bottom, and up to the South Rim. Many fewer people die this way.

Running the canyon “rim to rim” is a thing. According to the National Park Service, the trail “approximates a route used for millennia by many Native American groups.” It follows a natural break in the canyon rims. The trail was “built” in 1891 to reach mining claims, and it was turned over to the park service in 1928. Now the trail is mostly used by hikers and mules. But at least a few people run it every day during non-winter months, for reasons variously healthy and not.

The trail is visible in the center (Sarah Yager / The Atlantic)

Our group consisted mostly of my dad and his friends, who are semi-retired or tenured and so have decided to spend a not-insignificant amount of their time running. They had trained extensively. My own training consisted of running around Prospect Park in Brooklyn, which is a three-mile loop with one hill. Sometimes I did it twice, and twice I did it three times. The total distance across the Grand Canyon is around 24 miles. (Though measurements differ. By the end, my iPhone would register 48,890 steps, or 29.5 miles.)

In terms of ideal preparation, you would probably spend a few days acclimating to the elevation—the beginning is at 8,200 feet above sea level, before descending to 2,400 feet, and then back up. You would ideally train someplace where you can run uphill at a steep grade in sand for miles at a time in extreme heat.

The descent (James Hamblin / The Atlantic)

Running the canyon also involves carrying your own water. A member of my running party told me the story of 24-year-old Margaret Bradley, who died of dehydration while attempting to run across the canyon in 2004, apparently after running out of water on the trail. She had finished 31st among women in the Boston Marathon earlier that year. Park officials said at the time that the temperature in the shade was 105 degrees Fahrenheit.

The longest stretch between water spigots is seven miles—which is too long. To keep your body’s fluid volume up, you have to drink a lot, and if you do it in binges it fills your stomach like a water balloon, which isn’t well tolerated when you then try to run. Ideally you drink in sips every few minutes. So we took backpacks with water bladders that we refilled at every stop.

Drinking too much water is almost as dangerous as drinking nothing. It can put a person over the edge into hyponatremia, where the body’s sodium levels are so low that the nerves and muscles misfire, and the brain swells inside the skull and also ceases to function. Taking in a lot of salt is key—and glucose with it. That’s why there’s oral rehydration solution, which has all these things in medical-grade proportions. The most well-known version is sold as Pedialyte, but a lot of them come as powders that can be mixed with water. Oral rehydration solution is one of the most important medical advances of the modern era, in that it has saved unknown thousands of lives during cholera outbreaks.

(James Hamblin / The Atlantic)

To avoid the hottest part of the day, we got up before dawn and were on the trail just after 5 a.m. It was 50-some degrees as we covered the first few miles downhill, which felt amazing. It’s tempting to get going too fast downhill, which I did, and wore out whatever muscles I hadn’t prepared for downhill running, many of which would turn out to be necessary later for uphill running.

Beautiful as the sunrise was, it was ominous to watch the light start to break onto the path ahead of us. When we made it to a campground at the bottom of the canyon around 9 o’clock, the temperature was in the 80s. (It would later get to more than 100.) Around the water spigot, an experienced hiker who had come from the other direction told us that even though we were halfway, we hadn’t done anything yet. Then he laughed, like it was fun for him to say that.

There’s “lunch” available at the camp, which we opted into ahead of time, and it turned out to be a plastic bag full of an assortment of packaged foods—Oreos, pretzels, an individually wrapped white bagel, oddly a substantial sausage, and a few other barely-food things. There was one packet of oral rehydration powder, which apart from an apple was the only thing I didn’t give away. It would require a special kind of training for me to run this trail full of Oreos and sausage.

Crossing a suspension bridge over the Colorado River, the lowest point of the trail at 2,400 feet. (Sarah Yager / The Atlantic)

Another challenge is the squirrels. The first time I noticed a squirrel, I thought he might just be rabid. Though rabies in squirrels is extremely rare. When the second one started pursuing us down the trail, I knew something was up. Not long after, at a rest stop, we saw the first of several large signs that said “Do not feed the squirrels!” And then, in red: “Warning. Prevent Plague.” Plague? Yes. The animals carry fleas, which carry plague.

If the falling and dehydration weren’t enough, now there were the biting squirrels and plague. According to National Geographic, Grand Canyon National Park began its campaign against plague following the 2007 death of a National Park Service biologist. Having the squirrels close in around me at the water stops was the most threatened I felt on the trail.

By the most intense part of the ascent, it was noon. The climb up the South Rim is about six miles of sandy switchbacks, fully exposed to the sun. The last three miles were the toughest, though, for other reasons. I didn’t drink enough. I know this from the lack of urine output in the second half of the run, which is the best way to know you’re hydrated, or at least not going into acute renal failure. I’m sure I was. That view, though.

The ascent (Sarah Yager / The Atlantic)

A major factor in the fluid depletion was that, given the conditions, it really felt like sunscreen wasn’t enough. My skin was too soaked with sweat to really apply it effectively. It was like trying to paint a barn in the rain. So I covered all the skin I could with clothing—I wore a long-sleeve shirt and neck gaiter and cap. By the time I reached the top, all of them were coated in a film of white sodium. A desire to lick the salt from your clothing is another indicator that you’re way behind on intake.

It was bizarre to arrive at the top so haggard and find myself at the South Rim lodge, which is a major tourist destination. You can drive all the way up to the edge and buy ice-cream and then get back in your air-conditioned car, and that’s what hundreds of people were doing when I arrived. I don’t mean to sound superior in describing this. I really don’t know who would be superior in this situation. Like marathons, this wasn’t the sort of exercise undertaken to try to be healthy, but the sort you hope to be healthy despite having done.

Standing there at the South Rim, one of the ultra-marathon runners in our group said the ordeal felt similar in difficulty to a typical 50-mile trail race. The shower afterwards was in the top-ten best I’ve ever had, and even the horrible pizza at the lodge tasted amazing, and don’t get me started on the sleep. I can’t say that anyone felt or looked “good” at the top, or for the rest of the day. But there were no deaths in the canyon that day. To my knowledge.