America was full of giraffes, rhinos, local horses, mastodons, mammoths and a ton of other animals when first Mongoloids showed up
You are most probably talking about the Clovis people; 13,500 to 13,000 calendar years ago.
A little over ten thousand years ago in a much cooler climate as the remnants of the last Ice Age retreated, (other wise the Asian ancestors of the indigenous population of America couldn't have walked across the land bridge from Siberia to Alaska, then down to the rest of the continent.)
The Clovis people possibly weren't the first people in America because of discoveries in both North and south America which pre-date the Clovis discovery some date to ∼23,000 to ∼19,000 years ago.
Either way the die off took over 1000 years (maybe even more), and involved a heating planet, hence the glacial retreat.
The repeating rifle and commercial hunters managed to almost eliminate the bison (buffalo) on the plains in a little over 15 years.
Not the same ..... either by time frame or how the animals were used, the Bison were allowed to rot in place after skinning, where as the Clovis or other peoples couldn't afford to waste what they got from their hunt, which was essentially for food.
How cathartic it is to give voice to your fury, to wallow in self-righteousness, in helplessness, in self-serving self-pity.