The number of hikers visiting US national parks is increasing. So is the challenge of keeping them safe

The death of a young woman falling from the famous - and ever more popular - Half Dome in Yosemite ignites debate

In 1974, Scott Crollard, a teen on a church youth group trip, casually climbed cables to help reach the lofty summit of Half Dome, whose name describes a unique rock formation in California from which you can see the Yosemite Valley some 5,000ft below.

I remember sitting on the edge of the lip of Half Dome with my buddy and just gazing over the edge. And when he got off, he kind of nudged me, and I darn near fell off the thing just because we were so nonchalant about it," said Collard, now a 65-year-old retired emergency room physician in St Louis who again ascended Half Dome in 2017 with more appreciation for its magnitude.