On the southern rim of Newberry Volcano's 5-mile wide caldera lies the state's largest obsidian flow. At roughly 1,300 years old, the Big Obsidian Flow is the massive volcano's most recent eruption. This short interpretive trail offers incredible insight into the geological and human history of the region in addition to panoramic views of the rest of the caldera and the Three Sisters to the west.

In contrast to the igneous basaltic lava that is found throughout the Pacific Northwest, obsidian lava contains much higher concentrations of silica, the primary ingredient in glass. Add to this a touch of iron oxide and, once cooled, this lava solidifies into a deep black glassy rock. Not all of the lava in this field is obsidian, however. Obsidian eruptions tend to be quite explosive, and this gas-charged lava gives much of the rock its vesicular texture and grayish tone. In its purest form, this extremely high pressure, gas-charged lava will be ejected almost as a spray. The solidified form of this 'spray' is known as pumice, and it can be found in great abundance throughout the trail and lava flow. In comparison to other rocks, pumice is one of the lightest because of its average porosity of 90%, and unlike most rocks, when thrown into water it will initially float.

As far as humans are concerned, obsidian has long been prized for its sharp edges and its ability to easily be fractured into various and ideal shapes. Archeologist have discovered artifacts from the volcano Kariandusi in Kenya dating as far back as 700,000 B.C. Because of its use in trade, obsidian artifacts have been found throughout North America.

Note: Technically dogs are permitted on this trail, but due to the sharp nature of the obsidian it is highly discouraged.