Dawne Robinson and about 10 other searchers spent Mother's Day searching a hot, dry, boulder-strewn hiking trail for clues of what happened to her younger brother, who vanished last July at Joshua Tree National Park in California.

Paul Miller of Guelph, Ont., 51 at the time, was near the end of a hiking vacation with his wife Stephanie when he disappeared on July 13, 2018, after setting off solo to explore the difficult but well-marked 49 Palms Oasis trail.

In a phone interview Sunday from the same trail, Robinson said that she, her husband and friends kept searching -- with help from strangers -- to find out what happened so Miller's wife and two children can find some peace.

"They're all sort of clinging to the hope that, you know, maybe he fell and hit his head and has amnesia and maybe he's still going to come home eventually," Robinson said.

"So I think finding him would at least allow them to move on. It's the not-knowing, I think, that's hard."

There have already been extensive searches of the rugged terrain, both last summer after his disappearance and last November when Robinson and her husband continued on a smaller scale for nearly two weeks.

Even though Miller was physically fit and an experienced hiker, Robinson said the trail can be difficult to travel because it's so mountainous, dry and hot -- even in May, let alone July.

"Today, right now, it's supposed to get up to, I believe, 31 degrees (Celsius). But in July, it was even hotter. So when you're out here, you really have to drink a lot of water."

In addition, distances can be hard to judge and sometimes even big boulders look small until they're close.

"Some of these boulders are huge, like bus size and bigger," she said. "You have to look under things because it would be so easy for clues to kind of slip under into some of the crevices."

The conditions mean it's unlikely that Miller survived long, according to Robinson and professional searchers who spent five days looking for him last July before concluding that the heat was also a danger to themselves.

"There was a witness that saw him part-way in. The witness was on the way out. He said they spoke briefly. He said Paul was moving really fast, which made sense because I've hiked with Paul many times and he's a fast hiker."

The original search included a dog team that followed Miller's scent as far as the oasis.

"So we know he got at least that far. We're not sure what happened after that," Robinson said.

She added that, whatever happened, she hopes it was quick.

"The thought of him being in here, in the desert, it wouldn't be a nice way to go. Especially in that heat. I don't think he'd last all that long."

Even though no trace of Miller has been discovered so far, Robinson said she's determined to keep looking.

"He was my little brother. There was about 10 years difference. . . . But a very good friend, even though there were a lot of years between us."

"We liked the same things. He's into hiking, camping, white water sports. So we were pretty close."