318 IOWA ACADEMY OF SCIENCE 



For a distance of one-fourth to more than one-half of a mile 

 back from the Columbia, the ground rises only from four or 

 five to fifteen or twenty feet above the water. The soil is here 

 loose and shifting, largely of water and wind formation. Be- 

 yond this strip of lowland the country rises rather abruptly 

 two hundred or three hundred feet higher. This is about the 

 mean elevation of the territory as far to the southward as our 

 observations extended. There are higher points here and there 

 and numerous depressions, but on the whole the country is not 

 particularly rough. 



Two or three miles southeast of the town is the end of a long 

 lava ridge, extending for some miles to the southwestward. In 

 many places it appears double, as if it had been upheaved and 

 split. It rises from one hundred to two hundred feet above the 

 general level of the country. On the eastern side of this ridge 

 is a depression containing a chain of apparently perennial pools 

 or ponds, none covering an area of more than an acre at the 

 date of our visit. They are fed by small springs, and are all 

 rather strongly alkaline. 



On the west side of the Umatilla there is a considerable strip 

 of land of about the same elevation as that lying along the Co- 

 lumbia. This has mostly a gradual rise to the westward. 



On the whole, the area covered by these observations pre- 

 sents no great variety of soil conditions aside from water sup- 

 ply. The low strip along the Columbia and Umatilla rivers is 

 very sandy, much of the sand being loose and shifting. It has 

 doubtless been brought up largely from the sandy margin of 

 the Columbia by the strong winds that blow almost constantly 

 up stream. These winds sweep with great force across the angle 

 formed by the confluence of the two streams on the w r est side of 

 the Umatilla, and here there are many low shifting dunes. 

 Along the lava ridge the ground is, of course, strewn with frag- 

 ments of this material ; otherwise throughout most of the ele- 

 vated area the soil is made up mainly of water-worn gravel, 

 fine sand, and volcanic dust. In some places the vegetation in- 

 dicates the presence of a certain amount of alkali, but this is 

 not abundant except in the above mentioned depression where 

 the ponds are located. 



Aside from water supply, probably the most important factor 

 in determining the character of the vegetation in any of the 



