"I received a tip from my boss (at Sunset Color Nursery) that there was a waterfall and decided to go up and see if it was true," said Christianson, 17, a junior at San Ramon Valley High.
The first time he checked, it was dry. So he tried again after the big rainfall earlier this month.
"I took my dad when it was raining … we got there and the waterfall was gushing," he recalled last week. "I was shocked."
Christianson is no stranger to hiking and thought he knew what Las Trampas had to offer. He also found small cascades along the Hemme trial, just 10-15 minutes from the trailhead.
"Most of the hills are dry as a desert," he said. "You'd never think there could be a moist forest in Danville."
His family - mom Sandra, dad Ted and brother Alex - all enjoy hiking, he said, and treat Mount Diablo as though it were their back yard. They moved to Alamo from Minnesota seven years ago and, thrilled with the local terrain, have been hiking ever since.
His dad and Alex climb the big summits, such as Mount Shasta and Mount Rainier, and his father trains for mountain climbing with a 50-pound pack on his back.
"I want to climb Mount Whitney," said Joe. "The southern Sierra Nevada contains so much beauty."
He recommends hiking poles and says they are a well-kept secret that he conjectures his family may have discovered because his mom used to be a cross country skier.
"If you are coming down a steep slope, you don't want to ruin your knees," said Christianson. "If you're trying to get up a slippery slope, the poles anchor you."
They often hike on Mount Diablo and in Las Trampas.
"We hike so much we've become familiar with the trails," said Joe. "If I see a trail and it leads off somewhere, I'll follow it."
To reach the Camille Avenue waterfall, he hiked up through a small eucalyptus grove, then along a canyon - a hike that took about 40 minutes.
"I love to explore the hills around here," he said. "I often go on small photographic expeditions."
He brings his Canon PowerShot and posts photos at www.flickr.com/photos/parsectraveller/.
"It's capturing nature that a lot of people won't ever see," Joe said. "When I can capture it, they're often astonished that such beauty can be so close by."
His photos on the Internet include gorgeous butterflies and a rattlesnake found on Mount Diablo.
He said he has an obsession with science fiction and astronomy.
"I've always really been interested in the physical world in general," he said. "I like geography, which is probably the root of my hiking hobby."
He said when he was growing up in Minnesota, he wanted to be a tornado chaser.
"But I think the California weather has changed me," he said. "Now I really want to do a career involved in science and how it affects the world."
He's already discovered firsthand how torrential rains can turn dry local hiking spots into a forest primeval.