These ancient volcanoes provided the fine ash deposits and erosional outwash materials that became the Mascall Formation, forming 15 to 12 million years ago.
(These ancient volcanoes; provided; the fine ash deposits and erosional outwash materials) (erosional outwash materials; became; the Mascall Formation)
These ancient volcanoes erosional outwash materials
provided became
the fine ash deposits and erosional outwash materials
the Mascall Formation