I have spent a lot of time looking at scat, and if you'd like to learn the basics of how to differentiate some common types of scat, see this post. Today we'll go into a little more details about some of the scat found in the area. I've gone to the trouble of trying to draw some of the scat, although these pictures are not to scale. Mouse scat is nowhere near as large as mountain lion scat. Really.
Let's start with some of the bigger scat. Bigger animals leave bigger scat, and the biggest one in our area is the mountain lion. Much of the information that follows was obtained from the excellent book Scats and Tracks of the Desert Southwest by James C. Halfpenny along with observations I've made over several years (do I really want to admit that?). 
Carnivore Scat
[Image]Mountain lion scat
Mountain lion scat is usually about 1.25 inches in diameter, with pieces up to 4 inches long. The ends are blunt as is common for cats, although a drier diet produces more tapered ends. Like house cats, mountain lions occasionally bury their scat, with dirt scrapings around the scat. Bones and hair are usually obvious in the scat.
[Image]Bobcat scat
Bobcat scat also usually has blunt ends, but it is much smaller than lion scat, with a diameter of only 0.8 inches. Pieces can be three inches long, and dry scat falls apart. Bobcats sometimes cover their scat with dirt and other debris.
[Image]Coyote scat
Coyote scat usually has tapered ends as is common in the dog family. The scat is often dark in color but may be brown or gray with lots of hair and bones depending on the diet. Coyotes occasionally scratch near their scat piles to mark territory. Diameter is 0.6 inches and length about 3 inches.[Image]Gray fox scat
Gray fox scat is also tapered and can look very similar to coyote scat, with a diameter of 0.6 inches. Length is generally about two inches long. Scat color varies depending on diet, and may include more plant and berry material than coyote.
[Image]Skunk scat
Skunk scat also has blunt ends, but is smaller than mountain lion or bobcat scat, with a diameter of 0.25 to 0.75 inches. Length can extend from 1.5 to 5 inches. Insects are often a large part of a skunk diet and may be present in the scat, along with bird feathers, mouse fur, and carrion.
[Image]Weasel scat
Weasel scat is not easy to find. It's only 0.1 inches in diameter, but can be 1.5 inches long. It looks like a wavy, black cord with hair-like ends.
Herbivore Scat

[Image]Deer ScatElk are the largest herbivores in our area, followed by deer. Their scat is nearly identical in shape, but elk scat pellets are 0.5 inches in diameter and deer scat pellets are 0.3 inches in diameter. When the scat is moist, the pellets stick together. A drier diet allows the pellets to scatter when reaching the ground. The typical shape is called nipple-dimple, with a pointed end and a concave end, but drier scat is oval-shaped.

[Image]Rabbit scat
Rabbit scat is brown, round, and about 0.3 inches in diameter. Both the black-tailed jackrabbit and the desert cottontail also produce a black, semiliquid scat that they usually reingest for the remaining nutrients.
[Image]
Porcupine scat
Porcupine scat can be pellets or strings of pellets that are connected by fibers. In the winter, scat is often redder from feeding on conifers, and in the summer, brown to black from eating herbs and shrubs.[Image]Chipmunk scat
Squirrel and chipmunk scat is very similar, with small, unconnected ovals. Squirrel scat is 0.2 inches in diameter and chipmunk scat 0.1 inches in diameter.
[Image]Mouse scat
Mouse, pocket mouse, and vole scat all looks virtually identical: dark, small, oval, and unconnected. Voles have the distinction of leaving thousands of scat pellets in tennis-ball sized latrines. 
And that's it for today! But I'll be back again with more photos and info about the wonderful array of scat found in the desert southwest. I hope you'll be back again too!