My first guess for this smallish brownish terrestrial frog is Craugastor, because in Guatemala that's my first guess for all smallish brownish terrestrial frogs. I don't see anything that makes it look particularly non-Craugastor, but I also have been unable to find any lookalikes in this area in the references I've checked. There is also some possibility that it is Leptodactylus melanonotus, which is found nearby.

Here is a list of all the reptiles and frogs I saw on this trip to Guatemala.