Out here, well past the congested string of legendary surf spots with a view, this four-mile stretch of white sand and scenic tumult between the Kaena Point Natural Area Reserve and Dillingham Airfield is a favorite escape for urbanite campers and day-trippers.
It offers them a measure of isolation, serenity and beauty.
It pains Mateo to see people trashing it.
Mateo, who's employed by the state parks system to watch this coastline, including adjacent Kaena Point Natural Area Reserve, spends much of his time cleaning up.
The main object of his concern is a series of black squares dotting the beach, charred remnants of shipping pallets burned by campers for warmth and visual effect.
But the visual effect of the bonfire's aftermath is disgusting, say Mateo and other thoughtful beach-goers.
More importantly, though, the burned pallets pose a safety threat; the wood is reduced to ashes, leaving only nails and jagged metal connectors in the sand.
"It stays hot for two days," said Mateo, known informally as the ambassador of Kaena. "People just trash this place because it's so accessible. They drink their beer, throw their cans in and leave ... They never clean it up. It renders this piece of beach unusable."
Until Mateo moves in with his industrial-strength magnet and combs the sand for the metallic debris. He routinely pulls out nails by the gross; one day last week a burned spot yielded a 15-gallon pail full of them.
When he's not pulling cleanup patrol or tending to his duties at the natural area reserve, Mateo is likely spreading the word to campers.
Technically, it's illegal to have open fires on so-called unencumbered lands (parcels owned by the state but deemed substandard for park designation) because of the fire hazard, said Mateo.
But if beach campers insist on building fires, he suggested they use logs and dig pits that can be covered afterward.
But pallets, which campers get from supermarkets and other stores, seem to be the fuel of preference. So Mateo has been approaching North Shore establishments, asking them to control their pallet flow. And he's talking to as many campers as he can, requesting their cooperation. Mateo has no enforcement authority.
"My job is to interact with people to make sure they use the area properly instead of abusing it," he said. "People are still getting used to a guy coming up to them and telling them what not to do."
Most understand, although he's had a few minor confrontations.
"I've told myself, don't be discouraged," he said. "You can't change peoples' habits overnight. But I pick up trash in the same places every single day. Sometimes it gets a little discouraging."
But Mateo can't be too judgmental. He's been there.
"I used to come out here and actually do the things I'm telling people not to do," he said.
Pat Basilio and Mark Wagatsuma, who were among a large group of old friends camping at the beach over Easter weekend, took Mateo's diplomatic advice cordially: They'd continue burning the pallets they were given by a local merchant but vowed to approach their fires with care.
"We try to take out the nails before we start the fire and we try to dig it deep and bury it up after," Basilio said.
"I think more and more people are coming around to conservation," said Mateo, his beach rounds complete for the day.
But he'll be back tomorrow.