Up to 16 inches of rain fell in a dramatic thunderstorm that started at dusk and continued well into the night.
Most residents had no warning.
The resulting flood scoured the canyon and moved tremendous amounts of rock and debris. Houses and cars all just became a part of this "flow."
The vast majority of the 144 people killed in the flood were determined by the county coroner to have been crushed before they could drown.
Several victims were never found. This was particularly hard for those families.
The Big Thompson flash flood is known to flood experts all over the world. It is considered to be a rare event but could happen again at any time.
If such a flood were to hit Boulder, Colorado, the results would likely be far more devasting since so many more people live at the mouth of the canyon.