New Mexico is, perhaps, the worlds biggest classroom for the study of ancient volcanic activity. The "tuff" at City Of Rocks, New Mexico is a type of rock consisting of consolidated volcanic ash ejected from vents during a volcanic eruption. A great picture, and a great subject choice for NM. :)
A beautiful picture, but this is not an agave. It may be a Dasylirion wheeleri, sometimes known as the "Desert Spoon", or the "Sotol Yucca" (though, it is not actually a "yucca", either). Dasylirion species are sometimes used to make Sotol, a distilled spirit produced in a manner very similar to way agaves are used to make mezcal in Mexico.
These desert mountains are filled with such wonderful surprises! :)
Well put, as any who wander these trackless desert mountains can attest.