Give an example of geographic reproductive isolation

Mhmm ... there are two types of squirrels in the grand canyon, one (the kaibab) living in the northern rim of it and the other (albert's squirrel) in the southern rim

Populations can become separated by rivers, mountains, or bodies of water. A pretty common example of geographic isolation is a population migrating to an island and becoming separated from the mainland population. Over time, the two populations become reproductively isolated and they evolve separately.