Take a photograph of the rodent, if you can. This allows you to study it more closely at your leisure. Rodents are fast and unlikely to hang around while you examine their ears and tails.

Place the ruler next to where you photographed the rodent and take another picture. Compare the two photos to get a measurement of the animal’s length. You now probably have a choice of several rodents of a similar size in the identification guide, so you need to narrow it down further.

Look at the tail. Is it long, short, hairless, furry or very furry? You are now able to rule out several more rodents. For example, a rodent with a long tail is not a vole.

Look at the face shape. Does the rodent have a blunt or pointy face? The face shape allows you to eliminate several more rodents. Very small rodents may be mice or voles. Utah's mice, including the canyon mouse and the common house mouse, usually have pointed faces while voles have blunt faces. Larger rodents also have distinctively shaped faces. For example the botta's pocket gopher is the same size as a Norwegian rat but looks completely different because of its rounded, almost guinea pig-like face.

Look at the size and position of the ears. Are they positioned on the side of the head or near the top? The dark kangaroo mouse, for example, looks different to other mice partly because its ears are on the sides of its head.

Note the site. You should now have a short list of about two or three possible rodents. Compare their distribution maps and habitat. The species most widespread in the location of your rodent is almost certainly the solution, not a species last seen in the region 50 years ago.

Refer to pictures of other kinds of mammal in the identification guide if your animal does not look in the least like any of the rodents. For example, a tiny animal with a very pointed snout is not a mouse; it is probably a shrew.