At times the Absaroka volcanic eruptions were violently explosive, showering the countryside with rock bombs, cinders, and ash. The finer debris that reached the lower slopes of the volcanoes was reworked and carried by streams into the intervening valleys, where it was deposited as sand and gravel (fig. 16). Eventually the entire Yellowstone region was choked with volcanic debris, the material from one volcano mixing with that from neighboring volcanoes. Even the mountain masses uplifted during the preceding Laramide orogeny were covered by the vast accumulation (fig. 18). [Illustration: MASSIVE BEDS OF BRECCIA of the Absaroka volcanic rocks along the road north of Dunraven Pass. This breccia formed part of a steep-sided volcanic cone, of which Mount Washburn is a remnant. (Fig. 17)] [Illustration: Closeup view shows very coarse character of the breccia, with large rock fragments imbedded in fine ash, dust, and sand. Nearly all the rocks are of andesitic composition, consisting chiefly of feldspar and pyroxene. Most common colors are medium to fairly dark shades of brown, red, purple, and gray.] Absaroka volcanism, however, was not a simple, continuous process—the eruptions were intermittent, the many volcanoes were not always active at the same time, and between eruptions there were long periods of quiescence during which the erupted material was deeply eroded. The repetitive nature of the eruptions is best illustrated by the famous fossil forests of Yellowstone. Here is striking evidence that enough time elapsed between eruptions for widespread forests to become established on the lower slopes of the volcanoes and in the broad valleys between them. Judged from the great size of some of the now-petrified logs (fig. 19), several hundreds of years must have passed before another volcanic outburst smothered the forest. Many different forest layers have been recognized in the Specimen Ridge area as well as in several other places throughout the Park.