I guess there were a lot of them

 

While working on building a new airport near Mexico City, workers, and now paleontologists, discovered the skeletal remains of Columbian mammoths, the southern counterparts of the perhaps-more-famous woolly mammoths.

First they thought there were 70.  Now it's more like 200.  Apparently the site was the marshy shore of a lake where the mammoths either got mired in the mud, or moved slower while foraging and were easy kills.  A few human remains have been found with the many massive mammoths.

Site in Mexico City is dubbed 'mammoth central' after 200 skeletons are found

From the article:

"Columbian mammoths had very little fur, unlike their woolly cousins which lived in frigid tundra. The giants were up to 15 feet tall, wigged up to 22,000 pounds and had enormous tusks up to 16 feet long. They also had an estimated lifespan of around 65 years. They are one of the last lineages of mammoth to go extinct in the world and were wiped out around 12,000 years ago. The Columbian mammoth inhabited North America as far north as the northern United States and as far south as Costa Rica."