August, 1955 
Hill prairies are absent from the gener- 
ally northeast-facing slopes of the bluffs 
on the southwest sides of valleys; these 
slopes are covered by forests except where 
they have been cleared and are now in cul- 
tivation. 
Altitude.—A relationship apparently 
exists between height of the bluffs and oc- 
currence of hill prairies. More prairie 
openings and prairie strips are found on 
the Mississippi River bluffs in Pike, Cal- 
houn, Monroe, and Randolph counties 
where the bluffs are high than on those 
bluffs just north or south of Quincy in 
Adams County where the bluffs are low. 
At Clendenny prairie (Calhoun County), 
the bluff rises 220 feet above the bottom- 
land ; at Sessions ( Pike County), 240 feet; 
at Fults (Monroe County), 340 feet; and 
at Phegley and Sampson (Randolph 
County), 310 feet. The bluffs north of 
Quincy are only slightly more than 100 
feet and those south of Quincy are but 
120 feet above the Mississippi River bot- 
tomland. 
Parallel Tributary Valleys—Dur- 
ing the course of field work, the writer 
observed an interesting feature of the 
bluffs. In 34 of the 61 hill prairies vis- 
ited, tributary valleys are found approxi- 
mately parallel to and short distances back 
of the bluffs, fig. 5. In each of the 34 
sites, the area between the major stream 
valley and the parallel valley, or valleys, 
is a narrow ridge that is joined to the up- 
land beyond by another narrow ridge more 
or less at right angles to the bluff. Hill 
prairies grow on the upper slope of the 
ridge that faces the major stream valley, 
a slope referred to as the upper bluff slope 
or the brow slope. Narrow ridges of this 
type occur where streams have cut back 
into the valley wall and where, at ap- 
proximately right angles to them, their 
tributaries have developed. The tributary 
valleys, mostly parallel to the bluffs, are 
V-shaped and forest covered. 
Environmental Conclusions 
As the climate and soils of Illinois per- 
mit the growth of both prairie and forest, 
it can be concluded that certain geomor- 
phic conditions are accountable for the oc- 
currence of hill prairies on the upper bluff 
Evers: Hitt Prairies oF ILLINOIS 375 
slopes. Location, the place in reference to 
major stream valleys, and topography, 
largely the result of the geomorphic his- 
tory of the region, exert strong influences, 
or controls, that are responsible for the 
presence of hill prairies. The growth of 
grassland rather than forest on the upper 
bluff slopes is attributed to priority of oc- 
cupation by prairie species and to the 
xeric conditions that are produced by the 
combination of local exposure to the sun 
and to the wind (especially to wind mov- 
ing unimpeded across wide floodplains), 
the height of the bluffs above the adjacent 
bottomlands, the steepness and direction 
of the upper slopes, and the permeability 
of the substratum. Thus, the hill prairie 
community is the result of a complex set 
of conditions, the effectiveness of which 
is determined by lccation and topography. 
VEGETATION OF HILL 
PRAIRIES 
The typical vegetation of hill prairies 
is the bunch-grass type. In most places, 
Andropogon scoparius is the dominant spe- 
cies. In some places, such bunch grasses 
as Bouteloua curtipendula, A. gerardi, 
and Sorghastrum nutans are locally dom- 
inant. In order to learn about the vege- 
tation, its density, the ground space it oc- 
cupies, the foliage area or crown cover, 
the available space per plant, and the fre- 
quency of occurrence of species in plots of 
several sizes, the writer made detailed 
studies of hill prairie vegetation by means 
of plot studies in two prairies. He also 
made studies of some characteristics of all 
stands from species lists and field notes. 
Phegley and Sampson Prairies 
From the 61 hill prairies that he vis- 
ited, the writer chose Phegley and Samp- 
son hill prairies for the detailed vegeta- 
tional studies. “These areas are on the 
same bluff ridge. In their surface fea- 
tures, Phegley and Sampson prairies are 
typical of hill prairies. There is a rock 
ledge and cliff at their base. A stony slope 
lies above the rock ledge, and loess caps 
the bluff. Each prairie area possesses 
spurs and coves. At the time this study 
was made, prairie covered both the stony 
