PAPERS OX GEOGRAPHY AND GEOLOGY 187 



OUTLINE OF THE GEOLOGY OF THE OREGON 

 QUADRANGLE 



Arthur Beyax, Univebsity of Illixois 



Acknowledgment. — In the summer of 1923, under the 

 auspices of the Illinois Geological Survey, the writer 

 made a geological study of the Oregon quadrangle, a 

 brief resume of which is here presented. A more de- 

 tailed report will appear in the near future in regular 

 bulletin form, published by the Surv< 



ation. — The Oregon quadrangle comprises an area 

 of approximately 235 square miles in the northern part 

 of Illinois, about midway between Rockford, Freeport, 

 and Dixon. It is mainly in Ogle County, but includes a 

 narrow strip of territory in southern Stephenson and 

 Winnebago count: 



Drainage. — Rock RiYer enters the quadrangle at 

 Byron, near the middle of the eastern border, and flows 

 through the southeastern quarter of the area, past Ore- 

 gon at the south margin. The well deYeloped drainage 

 of most of the area is directly tributary to this Yolumi- 

 nous master river and its few large affluents within the 

 quadrangle, with the exception of a few headwaters of 

 Pecatonica RiYer along the northern border. 



Topography. — Dissection by the numerous streams 

 has progressed until most of the area is in topographic 

 late youth. The greatest dissection, which locally has 

 reached a mature stage, is in a narrow belt on both sides 

 of Rock RiYer and throughout a broader belt along Leaf 

 RiYer. a comparatiYely small stream that flows easterly 

 across the middle of the area to join the Rock a short 

 distance below Byron. The greatest local difference in 

 eleYation is about 250 feet near Oregon, which is not 

 much less than the maximum relief of approximately 

 300 feet for the entire quadrangle. The least dissection 

 is in the southwestern portion, where an area of seYeral 

 square miles is still an undissected till plain. 



Striking contrasts are exhibited in the topography of 

 this quadrangle, and between it and that of much of the 



1 Published by permission of the Chief of the Illinois State Geological 

 Survey. 



