Answer:
The correct answer is A) Speciation by Geographic Isolation
Step-by-step explanation:
Geographical isolation can lead to speciation because if some members of species gets isolated geographically from the other members of species then they can not interbreed with each other and due to geographical isolation, they get different habitat to live so new variation will occur in them so that they can adapt to their environment which lead to evolution of new species.
So here deer population is isolated by the formation of the canyon between members of the group which prevented interbreeding between them and due to their isolation in two different habitat they adapted differently and can no longer interbreed. So the right answer is A.