Nolina 'La Siberica'. Here it is peeking out of the vegetation at us...
Not a fully described species, but possibly the highest growing of the trunk forming nolinas - at least the Mexican ones. Very distinct - the way the leaves are held and have the terminal tuft, plus the spiraling petticoat of dead leaves.
These pictures were all taken at around 2850m give and take. I don't know how much further up it grows as there was another plant that kept us occupied for a while...