Rainbow Mountain is a ridge in the Andes southeast of Cusco, in southern Peru, striped turquoise, gold and crimson and standing above 5,000 metres. Almost nobody had seen it before about 2013. A glacier sat on the ridge until then, and the stripes came out from under it as the ice went. The colours are minerals. Each band is a different bed of sediment, laid down flat on an old sea, lake or river floor over millions of years. The collision that raised the Andes buckled the whole stack and stood it close to vertical, and erosion has since cut it open, so the bands run diagonally up the hillside. They read sharpest in low light and flatten under a high sun.
The walk starts where most mountains end, at a trailhead already near 4,700 metres. A few kilometres of switchbacks climb from there past grazing alpacas and the herders working them, and the air thins with every turn you take. The last pull is short and hard, and the full band of colour only opens when you come over the top. From the highest point the striped ridge runs off to the west and Ausangate stands behind it, 6,384 metres of snow and the most revered apu, or mountain spirit, in the southern Andes. The ground under your boots belongs to the Quechua communities of Pitumarca and Cusipata, who keep the trail and lead llama and alpaca caravans across these heights. A short extra climb past the viewpoint drops you into the Valle Rojo, a fold of rust-red hills stained by iron, where far fewer people bother to go. The mountain was nearly lost as soon as it was found. In 2018 a mining company was granted a concession over hundreds of hectares of this ground. The communities that live off it organised against the claim, the company gave it up within weeks, and the range around was made a conservation area the year after.