The headwaters of the White River begin in a vast maze of sandy canyons that fan out below the White River Glacier, located on Mount Hood’s south side. The geologic story here is surprisingly new. Few hikers making their way up the west rim of this maze on the Timberline Trail realize that much of what they see around them – including the ground they are walking on — is barely two hundred years old.
At about the time Lt. William Broughton of the Royal British Navy was sailing up the Columbia River in 1792, and giving Mount Hood its modern name, the mountain was just completing a remake of the entire south side in an eruptive episode that lasted for a decade, beginning in 1781. These eruptions produced an enormous amount of volcanic ash and debris that piled up to form the smooth slopes that Timberline Lodge is built upon, and that make up the gentle slopes of Paradise Park.
Eight-hundred-foot Crater Rock formed from lava at the center of the vents that produced these eruptions. The monolith stands today as an impressive reminder of the power that has once again gone dormant beneath the mountain. Yet, when the Zigzag and White River glaciers reformed on the upper slopes in the years after this eruptive period, they began to make quick work of the soft new ash deposits, with their glacial outflow carving the deep canyons we see today.

How much material has been removed by the White River in the 230 years since? This second image gives a visual sense. Within the White River Canyon, Mesa Terrace stands as a fragile slice of the valley as it existed after the eruptions, and loses ground each year to the two forks of the White River that straddle it. The eroded areas are shaded in tan.
Below Mesa Terrace, itself, is the pre-eruption valley floor, revealed along the eroded flanks of the terrace where the White River has exposed downed forests flattened by the eruptions. Buried for more than two centuries by hundreds of feet of ash and debris, they have been well-preserved, giving scientists insights into the mountain as it existed before.
Travelers along the Mount Hood Loop can appreciate where all of this eroded material has gone when they cross the sprawling, mile-wide White River floodway, downstream, where the river continues to reshape the landscape to this day.

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Image Description: The first image shows a maze of grey, sandy canyons below the snow-covered summit of Mount Hood, with the cascading White River Glacier at the head of the canyon. Blue Lupine bloom in the foreground, on the brink of the vast canyon. The second image shows the same scene, but with graphics to illustrate how the mountain once looked before these canyons had been carved into recent volcanic flows from eruptions that occurred just 230 years ago. An 800-foot lava formation called Crater Rock was created as part of these eruptions, and is circled near the top of the mountain,
Photo © WyEast Images (2026)












