THE TOPOGRAPHY AND HYDROGRAPHY OF ILLINOIS xHx 



water very quickly, and so leaves the river subject to low stages for 

 a large part of the year. 



The principal branch of the Sangamon is Salt creek. 



SALT CREEK 



Salt creek is formed by the union of North and South Salt 

 creeks. North Salt creek has its source between two large ridges of 

 the Bloomington morainic system in southeastern McLean county 

 near the source of the Sangamon. It passes southward through the 

 outer ridge and across the undulating plain south of it, to its junction 

 with the south fork. South Salt creek heads on the outer border 

 of the Bloomington moraine, and flows southwestward across a 

 gently undulating plain to a point 5 miles east of Clinton, where the 

 two streams unite to form Salt creek. Above their junction each 

 stream has a length of 25 to 30 miles. The south branch in its first 

 2 miles has a fall of 50 feet, and below this a fall averaging 10 feet to 

 every three or four miles. The north branch falls 80 feet in its first 

 4 miles, with a fall below this averaging 10 feet to every two miles. 

 From their junction the united streams pass westward through the 

 Shelby ville moraine, entering the outer border plain at Kenney, 

 eight miles southwest of Clinton. The general course of the creek 

 continues westward to its junction with the Sangamon 50 miles 

 below. 



It receives Lake Fork creek from the south about 5 miles above 

 Lincoln, Kickapoo creek from the north about 4 miles below Lin- 

 coln, and Sugar creek, also from the north, about 12 miles farther 

 down. ■ 



The valley of Salt creek is much broader below the mouth of 

 Lake Fork than above and it seems probable that a larger stream 

 occupied Lake Fork valley prior to the Wisconsin invasion than 

 that which occupied Salt creek valley. The latter appears to be 

 almost wholly a post-Wisconsin stream as far down as its junction 

 with Lake Fork. 



Below the junction the stream averages a fall of 10 feet to every 

 three or four miles, but in the lower two miles the bed has a fall of 

 20 feet. The bed and banks of Salt creek, like those of the Sanga- 

 mon, are without rock. 



CROOKED CREEK 



Crooked creek is the last western tributary of the Illinois. It 

 rises in Hancock county and flows in an irregular course, southeast, 

 into the Illinois River at a point 14 miles below the mouth of the 



(d) 



