Complex sentence: In 1912 about 16,000 acres were set aside which have become the Fort Niobrara National Wildlife Refuge, where sizable herds of buffalo, elk and Texas longhorn cattle are now kept.
Split into simpler sentences: In 1912 about 16,000 acres were set aside. This area became the Fort Niobrara National Wildlife Refuge, where sizable herds of buffalo, elk and Texas longhorn cattle are now kept.