GLACIAL BORDER OF SPOKANE 
363 
Soil Survey of Spokane County recognizes that the western half 
of the county was covered with Glacial deposits, first recognition 
of the glaciation on the basalt plateaux, as representing a period 
distinct from other glaciation of the region, was announced by 
the writer a little over a year' ago in a paper read November 2, 
1921 before the Columbia Section of the American Institute of 
Mining and Metallurgical Engineers. 
In this paper attention was called to erratic boulders, gravel 
and clay deposits found on the surface of Columbia basalt plains. 
The basalt to the north and northeast of the city, is in detached 
masses, while to the south and west it is continuous with the 
Columbia plateau. In these localities it is dissected to some 
extent by narrow valleys of Latah, Lake, Paradise and Deep 
creeks. All are level-topped with an elevation of about 2500 
feet. They bear the names. Pleasant Prairie, Peone Prairie, Five- 
mile Prairie, Indian Prairie, Sunset Prairie, Paradise Prairie, and 
Moran Prairie, in order from northeast to west and south of the 
city. The first three prairies mentioned are at present de- 
' tached from the Columbia plateau. In every instance clay and 
gravel and abundant erratic boulders of granite and quartzite 
are mingled with boulders of basalt on the level tops. There is a 
decided tendency to angularity in all these boulders. Most com¬ 
monly they are embedded in clay or gravel. The gravel beds are 
typical of all Glacial gravels, i. e., in places unassorted and in 
others showing the assorting action of the out-wash waters. In 
different localities the ice-action is different. In some places, as in 
parts of Sunset Prairie near Sunset Boulevard and on Moran 
Prairie from near Lincoln Park southward to the city limits, its 
effect is to scour the basalt with very little depositing action. On 
Thirty-ninth Avenue, from the Adams School westward to near 
Perry Street, a distance of a mile, a trench dug for city water- 
mains showed only hard basalt. Here and there, at considerable 
distances apart, are to be seen granite boulders which might 
easily have been carried by floating ice. This suggests that the 
Columbia drainage through the Spokane Valley may have taken 
this direction for a time. The want of river gravels may be ac¬ 
counted for by a lake (mentioned later) acting as a settling basin. 
The great ice-mass must have approached by way of the lowland 
