Complex sentence: There is no historical record recording that a blizzard ever hit Yellowstone on or around August 25 of any given year, and interviews with older employees indicate that the celebration was not held prior to the 1930's.
Split into simpler sentences: There is no historical record recording that a blizzard ever hit Yellowstone on or around August 25 of any given year. Interviews with older employees indicate that the celebration was not held prior to the 1930's.