Asquirrel population lives in an area. over many years, a river in that area grows wider and stronger,
eventually forming a canyon. the squirrel populations on the two sides of the canyon can no longer mate
with each other and ultimately form distinct species. this is an example of
a. differential speciation.
b. penultimate speciation.
c. sympatric speciation.
d. allopatric speciation.

The correct answer will be option- D.

Explanation:

The speciation or the formation of new species from the ancestral species takes place through three ways: allopatric, sympatric and parapatric way.

The allopatric speciation results in the formation of new species due to the isolation of the population due to geographical barriers.  In the given question, the squirrel is not able to mate and produce organisms as they got separated by river or canyon creating geographical barriers.

Thus, option- D is the correct answer.