In addition one such shield volcano, the 425,000- year-old Cloud Cap volcano, erupted on the north flank of Hood from a vent only 5 kilometers or less from Hood’s summit. Mount Defiance (about 500,000 years old) on the south side of the Columbia River gorge and Lost Lake Butte northwest of Mount Hood are two examples of shield volcanoes. While the Mount Hood edifice was growing, regional volcanoes of chiefly basalt and basaltic andesite lava flows formed. 26 east of Government Camp are formed of lava flows from this time period. Well-known landmarks around the volcano such as Gnarl Ridge, Lamberson Butte, Yocum Ridge, Illumination Rock, and the high rock cuts along U.S. Some sequences cover broad sectors others are relatively narrow and were probably buttressed by glaciers significantly larger than those we see today. Each sequence comprises multiple flows tens of meters to locally more than 100 meters thick. The broad flanks of Mount Hood cover an area almost 20 km (12.4 mi) in diameter and are formed of numerous sequences of lava flows that were emplaced between about 500,000 to 100,000 years ago. Gnarl Ridge lava flows from about 350 ka at base to 200 ka at top, Mount Hood, Oregon eastern flank. 500 ka to 100 ka – Construction of much of Mount Hood edifice, partial destruction, and eruption of regional volcanoes The youngest such volcano is the 7-km-long Parkdale lava flow whose vent lies about 12 km north-northeast of the summit of Mount Hood. In contrast to the long-lived activity at Hood, each of these regional volcanoes was active for a relatively short period of time.

In addition to Mount Hood, other volcanoes scattered through the nearby area have erupted during the past 500,000 years.

The last two periods of eruptive activity occurred about 1,500 years ago and in the late 18th century. Similar deposits were probably formed in Mount Hood's past but were largely eroded, especially during ice ages, and are poorly represented in the geologic record. Much of the Mount Hood edifice is formed of lava flows, but eruptive activity during the past 30,000 years has been dominated by growth and collapse of near-summit lava domes to produce broad fans of pyroclastic flow deposits. Mount Hood, which has been active for at least 500,000 years, occupies a long-lived focus of volcanic activity that has produced ancestral Hood-like volcanoes for the past 1.5 million years. The shadow of the summit of Mount Hood, Oregon on a morning cloud bank.