_Kimberly Dike._ The low bluff across the river is formed by a vertical
dike of basalt which is about 60 feet wide. This dike cuts through the
John Day Formation and, farther north, the Picture Gorge Basalt (Fig. 8
). It crosses the river valley diagonally and can be traced nearly four
miles. The dike is formed of once-molten rock that “froze” in a fissure
which was a channelway for lava that fed a flow on the earth’s surface.
Many similar dikes are visible along the road east of Kimberly. The
basaltic magma is believed to have originated at depths of 40 miles or
more within the part of the earth called the mantle.
(At 105.3 turn east on State Highway 402 along the North Fork of the
John Day River)
[Illustration: Fig. 8.—Basalt dike two miles south of Kimberly.]