I hadn’t been aware of them until I came across this photograph.
There’s no Wikipedia article about the mountains which is almost enough in itself to convince me that this is a late, late April Fool.
However, Flashpacker.connect apparently organise day trips (but does that name sound like a hoax or am I growing ever so slightly paranoid?). They say:
Throughout your journey you will pass through a vibrant green valley with the impressive Ausangate mountain towering in the distance….As you get closer to the Rainbow Mountain you will begin to see the first signs of the colored minerals that formed the painted hills.
The travel blog Endless Adventure described it in 2015 as a secret place, hidden high within the Andes, but I was finally convinced of its existence when I did an internet search for Vinicuna, its Peruvian name, and I found that it had its own facebook page HERE So it must be real….