As the second day of searching for two missing Costa Mesa hikers ended, resident John Sendrey decided it had gone on long enough.

The 42-year-old IBM programmer thought a data- and technology-driven approach could be the key to finding Kyndall Jack, 18, and Nicolas Cendoya, 19. He took four buses and rode his bike to get to Trabuco Canyon armed with his iPad, iPhone and computer.

"My plan was to go out there, not to do the actual search … but to implement the technology out there," Sendrey said.

Instead, wearing Topsiders and mud-caked jeans, he became one of the first people in the protracted hunt to spot the lost woman Thursday morning, pointing rescuers to her perch on a nearly vertical precipice.

Sendrey, a Costa Mesa resident, spent Wednesday getting the lay of the land, visiting the official command post and later biking toward the trailhead. He urged other hikers, to no avail, to track their progress on virtual ArcGIS maps that illustrated the rugged terrain that concealed the two for so long.

But perhaps his presence made a difference anyway. Wednesday night, out of chaos emerged order, with volunteers organizing where to look next.

One volunteer donated a large white map that illustrated where hikers had headed and where they were most needed.

Another, Jeff Polaski, who also serves as a volunteer firefighter, organized groups of hikers by the level of their expertise, gathering names and phone numbers.

As night fell, the dusty impromptu gathering point got quiet. Many people left, while others hunkered down in their cars. Sendrey, a father of three young boys, brought no car to camp in and spent the sleepless cool night studying the maps.

Wearing just a jacket, he imagined what Jack, unprepared for four nights in the wilderness, must be experiencing.

"At least I had the company of the light and the bugs attracted to it," he said.

About 4 a.m. after hours of studying the map, it all made sense. Sendrey gleaned information on areas unexplored based on information from various maps, hiker locations recorded and reports of what Cendoya said.

"It's almost like the map was talking to me," he said.

Under a crescent moon he set out, biking to a point that ended up being about a third of a mile from Jack.

He climbed a ridge, thinking that as in chess he needed scope. He needed to be able to shout into canyons on either side, and maximize where his voice could travel.

"If I commit myself to a canyon, I'm effective in that canyon only," he thought. "That became my strategy."

He was discouraged seeing how little area he traveled over the rugged landscape, mapping points on his GPS. Before long he discovered which plants had shallow roots and which ones he could grab ahold of.

He shouted a variety of phrases. Sometimes it was "Hello?" Other times it was "Yo" or "Marco," anything to elicit a response.

He finally got one: "What?"

Cautiously he headed in the direction of the voice, unsure if he was hearing the lost hiker. He texted his whereabouts to Polaski, who then relayed that information to law enforcement officials.