The Idaho historian John E. Rees records that the old crater of Buffalo Hump was in a state of eruption as late as 1866.

If, however, we assume that the last manifestation of volcanic activity over any extensive area in Idaho was contemporaneous with the discovery of America, we will be as close to the truth as can ever be determined wiht any certainty. There can be no question as to where the ages of fire last operated in Idaho; it was in the lava beds of Blaine and Butte Counties.

The first mention of these lava fields in history is found in Washington Irving's "Adventures of Captain Bonneville":
"An area of about 60 miles in diameter, where nothing meets the eye but desolate and awful waste, where no grass grows nor water runs, and where nothing is to be seen but lava"

Of this area, a tract comprising some eighty square miles has been set aside by the National Park Service under the name of "Craters of the Moon National Monument". It forms the largest of the national monuments, and is the only national park or monument in Idaho. The name was adopted not because of resemblance to the actual surface of the moon, but because of similarity to the appearance of the moon as viewed through a powerful glass of that time. The Idaho field at it's highest point is around 6,500 feet above sea level and the craters are relatively small.

The Craters of the Moon are of particular interest ton historian because they are the most recent part of the great lava fields which form or underlie hundreds of square miles of the surface of Idaho and which, reaching to the westward, merge into the vast Columbia River plateau. Cold and black as they are now, it is easy to imagine them smoking, molten and mobile.

The smoke of the last flow of the Craters must have been visible for long distances in almost every direction. Cinder cones of various sizes and heights rise among the barren stretches of black rock, scrub and limber-pine and aspen trees are scatterd singly or in groups. It is easy to trace ancient rivers of molten mineral, their channels winding around obstructions, dropping in cascades and falls, appearing as if instantaneously frozen while still in motion.

The area can give you the erroneous impression that it must have been the scene of violent volcanic eruptions, but the lava beds are the result of comparatively quiet flows rather than of explosions.

Geologist Harold Stearns theory is that a tremendous fissure opened in the adjacent mountain slopes, from which the lava flowed out over the plain, carrying on its surface fragments of the lighter granite. The temperature of the basalt he estimated at 2,000 degrees Fahrenheit. The pressure being somewhat relieved, the fissure healed over, but from time to time at long intervals it again opened up and covered the area with a new surface of molten basalt. At least thirty distinct flows have been identified; scores of earlier ones are doubtlessly buried under those more recent.

The intervals between thes flows were so great that trees took root and sometimes grew to large size before a new flow surronded them. Frequently the enveloping lava would not destroy or even greatly deface a tree; in time the wood the wood rotted away, leaving a perfect tree-mold in the harden rock.

The last flow is estimated between 300 to 1000 years ago.

An Indian Legen
From the files of the Idaho State College Historical Museum
The Indians say their Great White Father had set the area we know as the Craters of the Moon aside as a private and sacred hunting ground. He forbade Indians to hunt there, and said that if they did so, the craters would soon become active and spread desolation over the area. One time a party of white hunters sought game in the region, even though the terrified Indians tried to dissuade them. As a result of the desecration, the Craters ame alive and spouted fire and covered the area with molten lava. And such was the cause of the last eruption.

Sources:
"Idaho: The Place and Its People" by Bryon Defenbach
"History of Idaho" by James H. Hawley
"IDAHO Legend and Story" by the Pocatello Chapter of Idaho Writers' League 1961