Read this: Simultaneously with these conflicts, bison, a keystone species and the primary protein source that Native people had survived on for centuries were being destroyed. Some estimates say there were over 13 million bison in Montana in 1870. In 1875, General Philip Sheridan pleaded to a joint session of Congress to authorize the slaughtering of herds in order to deprive the Indians of their source of food. By 1884, commercial hunting had brought bison to the verge of extinction; only about 325 bison remained in the entire United States.

About how many bison were in Montana in 1870?
What is the answer? (If it cannot be answered, return "unanswerable")
over 13 million