At 11:37 p.m. on August 17, 1959, a magnitude 7.5 earthquake rocked Montana's Yellowstone country.  In an instant, an entire mountainside fractured and thundered down onto the sites of unsuspecting campers.  The mammoth avalanche generated hurricane-force winds ahead of it that ripped clothing from backs and heaved tidal waves in both directions of the Madison River Canyon.  More than two hundred vacationers trapped in the canyon feared the dam upstream would burst.  As debris and flooding overwhelmed the river, injured victims frantically searched the darkness for friends and family.  Acclaimed historian Larry Morris tells the gripping minute-by-minute saga of the survivors who endured the interminable night, the first responders who risked their lives and the families who waited days and weeks for word of their missing loved ones.