Words from David: "We chose the most experienced West Texan cowboys we knew and they travelled west to Arizona with their lead horses. But we then encountered a massive and unexpected problem - the cowboys - who are as tough as old boots, felt the ride up the cliff face was too challenging for their horses. That offers some context as to why the end photograph here is authentic; it is a problem to get horses up to the top.

"Our unlikely solution was to ask the Navajo locals to ride their mustang horses up the mountain. After all, it’s their land and only they know the safest route to the top. The Texan cowboys meanwhile hitched a lift in the 4-wheel drive and were teased by me for not being up to the challenge."