Some of these videos are NOT from the New Mexico area, but they give an idea of the process.
There are many technical approaches to graffiti and murals. Some of the images are projected onto the surface and then traced, to be filled in later. Others are painted directly, either with spray cans or good old fashioned brush and paint. Many of these artists also use stencils, or they combine several techniques. Some require scaffolding to paint multi storied buildings—for less extreme needs, a portable elevator is used as you’ll see in the second video below.
Here’s good old fashioned brush work. Astounding art work. Call it what you may.