Geological Survey Professional Paper 644—F History of Snake River Canyon Indicated by Revised Stratigraphy of Snake River Group Near Hagerman and King Hill, Idaho

The foregoing account of the volcanic eruptions and associated drainage changes that produced the present Snake River canyon between Hagerman and King Hill leaves some matters still incompletely explained.

Not all the ground water, for example, that emerges as springs from lava flows along this part of the canyon exactly fits the changing pattern of drainage outlined here, even though the positions of most springs are understandable in these terms. The cause of the small discharge from McKinney Basalt at Bancroft Springs, in particular, will remain a mystery until drilling penetrates the concealed lava dam west of Bliss and reveals its character,

A progressive increase in the roughness of lava flows that erupted at various time during entrenchment of the Snake River corresponds with their decreasing age (the older flows being smooth and the younger ones being rough), but the McKinney Basalt is locally an exception, Smooth McKinney rimrock southeast of Bliss, which must be related to pillow lava in the canyon below, contrasts with rough McKinney elsewhere.

In a larger sense, the slightly weathered appearance of the McKinney Basalt (and the Wendell Grade Basalt) must be reconciled not only with the 30,000 years that has elapsed since the Bonneville Flood but also with whatever additional time was required to cut the Snake River canyon west of Bliss. Even though the McKinney locally displays patterned ground, a mark of the Pleistocene, its physiography is that of a lava flow which has erupted recently. Thus, together with the Wendell Grade Basalt of similar appearance, the McKinney provides an example of how little geomorphic change might be shown by other upper Pleistocene lavas in this region.

Preservation of the cascade of Wendell Grade Basalt along the canyon wall east of Hagerman is quite unexpected, especially because of the erosion that would be anticipated at neighboring sites of springs. Perhaps, however, this lava cascade is not at all anomalous; perhaps it demonstrates clearly enough that erosion along canyon walls rimmed with basalt—even a canyon supplied with local springs—is slow,