there's no reference to provide, because it isnt an auto fail. auto fails only exist on attack rolls and saves, and thats why you'll find references there. pathfinder is a permissive system, so you do only what it says specifically, and since you wont find details about this in the text for caster levels or dispel magic, a nat one isnt an auto failure.
this is the attack roll text:
Automatic Misses and Hits
A natural 1 (the d20 comes up 1) on an attack roll is always a miss. A natural 20 (the d20 comes up 20) is always a hit. A natural 20 is also a threat—a possible critical hit (see the attack action).
this is the saving throw text:
Automatic Failures and Successes
A natural 1 (the d20 comes up 1) on a saving throw is always a failure (and may cause damage to exposed items; see Items Surviving after a Saving Throw). A natural 20 (the d20 comes up 20) is always a success.
both are from the combat section on the pfsrd, if you'd like. you wont find similar text in any other ability, because you don't do the same thing in other abilities. so you won't find a reference for this specifically for dispel magic, because pathfinder doesn't spell out negative rules like that. hope that helps.
Does it say there are automatic failures for caster level checks?
No it doesn't.
Caster Level checks are described in several places as 1d20 + caster level with no mention anywhere of an automatic failure or success.
Here is the link to dispel magic for you.