The avid hiker known for leading Boulder Singles Hikes passed away Thursday on Mount Sopris.
Bob Baumgartner was 73 years old.
Baumgartner was hiking alone and apparently had a heart attack, according to The Boulder Singles Hikes website.
"He died doing what he loved," Judi Dressler posted on the website.
"He was a sweet, gentle soul who loved adventure and nature, and made it his priority to be out as much as possible and to get others out to enjoy nature as well," Dressler told 7NEWS.
"Bob, who led over 3000 hikes for almost 25 years, didn't screen people and took whoever showed up at the Boulder Public Library lawn, attracting thousands of people to his hikes from around Boulder County and beyond," said Dressler.
"One of his joys was introducing hiking to many people who had never hiked before. Another great joy for him was matching up singles, many of whom ended up getting married and in other relationships. He made tons of friends through his hikes... He was truly one of a kind," Dressler said.
All hikes have been canceled. However, a group of people were still planning on going on the "Lunar Eclipse" hike he planned, which was scheduled for 7 p.m. Sunday, Dressler told 7NEWS.
Two women found Baumgartner unconscious just below the false summit of the mountain and called for help, the Aspen Times reported. Dispatchers gave the women instructions and they performed CPR, but couldn't save him.