When did the Yellowstone caldera erupt?

During the summer of 1988, about 250 separate fires broke out in the greater Yellowstone eco-system. Most burned themselves out without causing noticeable damage. Seven fires became much larger than the others, and caused 95% of the nearly 800,000 acres of damage that summer. The largest, named the Shoshone Fire, was first noted on June 23, but it remained a minor event until about July 20.

Fire suppression after late July cost $120 million but did almost nothing to even delay the spread of the fires. Snowfall on September 11 finally ended the major damage, although the fires were still smouldering into November.