trends southeastward, it is the valley through which 
Apple River flows from this area, not into it, as would 
be the usual condition. 
Before the advance of the Winnebago glacier, 
the earliest of the Wisconsinan stage (the latest 
stage of the ice age), Apple River flowed from the 
northwest to the southeast and possibly continued to 
the east through a valley now partly occupied by 
Yellow Creek in Stephenson County. Such a flow 
would readily explain the wider valley to the south- 
east. The Winnebago glacier blocked the southeast 
outlet and impounded the water. The impounded water 
cut a new channel to the southwest. This channel 
drained the valley from the northwest and also drained 
the blocked valley to the southeast. Upon deglacia- 
tion, Apple River continued to use this channel to 
flow southwestward and to empty into the Mississippi 
River. 
The canyon is in a driftless area, one of the 
unglaciated parts of Illinois. The rocks exposed 
along the canyon walls are Ordovician in age, about 
400 million years old. 
Apple River Canyon has a vegetation of decidu- 
ous forest with northem coniferous representatives, 
prairie remnants, and an interesting cliff flora. Among 
the coniferous representatives are white pine and 
Canada yew. The forest contains such deciduous 
trees as white oak, northern red oak, Hill’s oak, bass- 
wood, hop hornbeam, and rock elm. Prairie is repre- 
sented mostly by remnants along the roadsides near 
the park and by a few remnants of the dry prairie 
type on the ridges. Big bluestem, little bluestem, 
Indian grass, and sunflowers are reminders of a more 
widespread prairie. The rare bird’s-eye primrose 
grows on some of the cliffs, fig. 3. One cliff is so 
much adorned by this_plant that it is known as ‘‘Prim- 
rose Cliff?’ (Pepoon 1917). This rare plant also grows 
on cliffs farther upstream, outside the park boundary. 
Studies of the plant life have been published by 
Boewe, Barrick, & Hague(1935) and by Fuller (1946), 
as well as by Pepoon. 
Disturbance by visitors in the park is present 
but not yet acute. Some pressure on the facilities 
provided in this park has been removed by the open- 
Te 
i 
___ Fig. 3.-- Apple River and the Primrose Cliff in Apple River Canyon State Park, Jo Daviess County. In early May, the 
cliff is bedecked with many pinkish blossoms of bird's-eye primrose. 
