48 GEOLOGY OF SW. TDAHO AND SE. OREGON. [bill. 217. 
JORDAN CRATERS. 
In the east-central part of Malheur County, Oreg., and from 18 to 20 
miles west of the Idaho-Oregon boundary, there are four recently 
extinct volcanoes, which are here termed, collectively, the Jordan 
Craters. They are situated to the north of Jordan Creek, and to the 
west of its tributary known as Cow Creek. The four craters referred 
to are nearly on a line bearing a little west of north and are approxi- 
mately 3 to 5 miles apart, although the distance of the one at the 
north from its next neighbor is somewhat greater than the spaces 
between the others in the series. While but four recent craters are 
here referred to, there are certain rounded hills to the west of the 
south end of the series which are probably of volcanic origin, and 
perhaps represent ancient craters, but these have not yet been 
examined. 
Three of the four craters referred to — that is, all but the most! 
northerly in the series — are situated in a valley, and the lava which 
flowed from them spread in all directions and built up lava cones with 
broad bases and low surface slopes. Each crater rises about 500 feet 
above the plain, but by far the greater part of this elevation is gained 
in the broad, low lava slopes surrounding the small buttes which mark 
the centers of eruption. The central elevations are in general about 
150 feet high, and are composed of lava which occurs mostly in thin 
sheets. There is an absence of scoria in detached clots and of lapilli 
or other ejected material, such as is blown into the air during explosive 
eruptions. In short, they are elevations formed by the cooling and 
hardening of lava which overflowed from the summits of volcanic con- 
duits in all directions, so as to form low cones with immensely 
expanded bases. When seen in profile, especially at sunrise or sun- 
set, they are at once recognized as typical examples of what I have 
ventured to term lava cones in distinction from elevations built by 
the accumulation of projectiles. 
The central and summit portion of each of the Jordan Craters is 
usually circular, with steep outer slopes, and in one instance contains 
a crater-like depression. This cavity in the summit of the cone, as 
in the case of many similar lava cones in Idaho and Oregon, is due to 
the falling in of a dome-like structure composed of thin lava sheets, 
the subsidence being caused by the escape of still liquid lava laterally 
from beneath a rigid crust. 
It is convenient to designate the Jordan Craters by numbers, begin- 
ning at the south end of the series and proceediug northward. A 
brief examination serves to show that No. 1 is the oldest in the series: 
next in age is No. 3, then No. 2, and last and youngest of all, No. 4. 
Their relative ages are shown by the degree to which their surfaces 
are weathered and the extent to which they are covered with soil and 
vegetation. The slopes of the oldest crater are smooth, with but few 
