The park's basin, or caldera, was formed by ancient volcanic eruptions brought about in part when North America's western crust rammed into the slower moving eastern crust.
(The park's basin, or caldera; was formed; ) (ancient volcanic eruptions; brought about; L:in part; T:when North America's western crust rammed into the slower moving eastern crust) (North America's western crust; rammed; into the slower moving eastern crust)
The park's basin, or caldera ancient volcanic eruptions North America's western crust
was formed brought about rammed
L:in part T:when North America's western crust rammed into the slower moving eastern crust
into the slower moving eastern crust