People feared that automobiles would frighten horses and wildlife, so the park superintendent issue a general order forbidding cars. .... Despite this several vehicles entered the park by accident or contrivance.
Automobiles
A Tale: Nights of Romance in Yellowstone Park — 1919
"Pop suddenly slipped and nearly tumbled into the hot water that lay on the thin crust of the basin. He grasped frantically and in so doing kicked the girl's foot so as to shove her towards Win."
A Tale: Touring Yellowstone Legally by Car — 1916
"When the new National Park Service took administration from the Army in 1915, they allowed cars—an action that transformed the Yellowstone experience."
A Tale: Yellowstone’s First Car — 1902
When Henry G. Merry tried to pilot is Winton past park rangers, they mounted up and gave chase. They lassoed the car and dragged it to the Park Superintendent.
M. Mark Miller, Author 