The lung-searing ascents into the Andean highlands aren't what worry the untold hundreds of young men who hump backpacks loaded with drugs out of the remote, lawless valley that produces about 60 percent of Peru's cocaine.

Armed gangs, crooked police and rival backpacker groups regularly rob cocaine's beasts of burden on their three- to five-day journeys over mountain paths carved by their pre-Incan ancestors.

In this country that overtook Colombia in 2012 as the world's No. 1 cocaine-producing nation, Mardonio Borda regularly hikes within a few hours of the Machu Picchu tourist mecca, bound for Cuzco with drugs.

The 19-year-old Quechua native has a sixth-grade education and speaks broken Spanish. But the 11 pounds of coca paste he carries will fetch up to $250,000 on New York streets as powder cocaine sold by the gram.

Hauling cocaine is about the only way to earn decent cash — $150 to $400 per trip depending on the load — in a region where a farmhand earns less than $10 a day and the poverty rate is triple the national average.

Yet it is packing highlands prisons with young, mostly native Quechua speakers who, like Borda, hail from the isolated communities that suffered the worst atrocities of Peru's 1980-2000 conflict with Shining Path rebels.

"The great majority haven't finished high school," said Laura Barrenechea, a sociologist who oversaw a study last year of 33 imprisoned backpackers. "They are not really conscious that they are the first link in the drug-trafficking chain."

The Apurimac, Ene and Mantaro river valley stretches northward for 250 miles (400 kilometers), and about a third of the coca grown here is trekked out by backpackers. Not a single fully paved road reaches the valley, which separates the Andes ridge from the Amazon basin.

Police say more and more cocaine is being processed to powder rather than left as coca paste, which includes residues of hydrocarbons, typically gasoline, used in initial processing. While authorities say most of the drugs are now flown out, the backpacking is dependable in the rainy season, cheaper than hiring a pilot and plane — and key to evading police checkpoints.

Backpackers, or "mochileros," ("mochila" is Spanish for backpack), have been hauling the drug for nearly two decades, traveling in groups as small as four and as large as 70. Guards with assault rifles often accompany them. They tote radios and satellite phones, while police rarely have more than cellphones.

Some backpackers carry handguns, some grenades.

Nobody hits the trail unarmed, they say.

Alcides Martinez, 24, lost two close friends. One fell off a precipice in the confusion of an armed robbery. Another was deemed an informant — and took two bullets to the head.

Many backpackers believe their bosses sometimes dispatch robbers — or sacrifice a small group to police so a much larger contingent can pass unperturbed carrying far more cocaine.

One said he invested in a load to try to get ahead and his boss hired thieves to steal his 25-kilogram (55-pound) share — then demanded he pay for the stolen drugs. The backpacker moved with his parents to the Pacific coast, where they harvest rice. Two years later, they still haven't paid off the $10,000 bank loan they took out to invest in the drug shipment.

"I can't go back," he said, speaking on condition of anonymity out of fear. "They said they're going to kill me."

Rural medic Oscar Huaman runs a health post along a principal backpacker route and sees mochileros almost daily.

He said robbers like to pounce at mountain streams when fatigued mochileros drop their loads to refresh.

In January, Huaman had to pluck grenade fragments from the legs and faces of two backpackers who were attacked at a stream. One lost his pack and the nearly 18 pounds (8 kilograms) of cocaine inside.

It could have been worse. Villagers along the remote routes sometimes run across putrefied corpses. Deaths go unreported. Bodies lack identification papers, and locals quietly bury them.

Borda, the backpacker whose route passes near Machu Picchu, says his group of four was once confronted by five gunmen.

"We only had three .38-caliber pistols," he said. "So that they wouldn't kill us, we gave them all the backpacks."

In highlands prisons near the Apurimac river valley, nearly half the inmates are in for cocaine trafficking — compared to a fifth nationwide. Worse for backpackers, a statute was amended last year to strip those newly convicted of drug offenses of a chance at parole.

President Ollanta Humala lamented the imprisoned backpackers' plight in remarks in Cuzco last July.

"I'm embarrassed for this country because we have not offered them opportunity."

Sociologist and drug war analyst Jaime Antezana said cocaine backpackers are disproportionately penalized because powerful traffickers evade prosecution by bribing police, prosecutors and judges.

"The policy is basically concentrated on the masses, on the narco lumpen proletariat, which is the backpackers. And they end up jamming the prisons."

Some backpackers long ago graduated to the big leagues of trafficking, moving to Bolivia to buy small planes and join the airborne-smuggling business, said Gen. Vicente Romero, Peru's No. 2 cop.

Borda has a more humble ambition.

He is saving up to buy land and get in on the ground floor.

"With coca bushes of my own," he said, "I'll earn more money."