A loose scatter of dry, pale balls on bare dust, some sitting alone, some in small clusters. Look close, or pick one up: a slightly squashed sphere, matte, pale to medium brown, giving off almost no smell. Break it open and the inside is dry, compacted plant fibre, closer to sawdust than to anything you would call waste. That is rabbit, jackrabbit or cottontail, and the scatter itself is already half the identification.
You will meet them most often out on the open bajada, on bare dust near the low blackbrush where rabbits feed and rest. The pellets are the one to learn first.
Which rabbit is a question of diameter and very little else. Jackrabbit pellets run larger, roughly 10 to 17 mm across; cottontail pellets are smaller, about 5 to 11 mm. Same shape, same dry texture, just a size class apart. The two ranges brush together near 10 or 11 mm, so don't hang the call on a single borderline pellet. Find the clearly oversized ones in the scatter and let those decide.
The dryness has a reason worth knowing. A rabbit or hare makes two different droppings. One is a soft, dark, shiny night pellet it eats directly from itself and sends through the gut a second time, pulling out the nutrients a poor first pass left behind. The other is this one: the hard, fibrous day pellet, the finished waste after everything usable has been taken out twice. You almost never find the soft kind, because it is re-eaten on the spot. So what lands on the ground is dry and nearly odourless for a plain reason. It has already given up everything it had.
Tell it from its neighbours by shape. Rodent droppings are smaller, darker, and harder, grain-shaped and pointed like dark rice, not round fibrous balls. Deer leave pellets that are oblong and acorn-like, dimpled at one end, dropped together in a single clustered mass. A rabbit passes one pellet at a time, so its sign arrives across the ground as a scatter, not a pile.
Which of the two it was, a single scatter often cannot say, and much of the time knowing it was a rabbit is enough.