The collision occurred just East of the bridge over the Olean Creek. I believe that a portion of the derailment made its way down the bank, into the creek-bed itself.
The (Westbound) train had parted someplace in Hinsdale. The crew was apparently unaware of this, and as the front of the train slowed for Olean, the rear end caught up with the front, causing a derailment and fire. The explosion actually occurred quite a while after the initial derailment, which gave the people of North Olean (mainly boys and young men) plenty of time to gather near the derailment and fire.
My Grandmother witnessed the aftermath of the explosion, seeing many of the deceased, awaiting pick-up by their families.