The Physical Environment 

 topography oe the sand region 



Over most of the sand region the topography indicates that other 

 agencies than wind have been at work. The ridges extend in a direc- 

 tion roughly parallel with the river, often being more than two miles 

 across. They rise gradually from the plain, the highest points, near 

 the middle, being usually about fifty or sixty feet above the general 

 level. The surface of the ridges has been modified by the wind into 

 dunes and blowouts, and aside from the general ridge-like form pre- 

 sents the appearance of a typical dune-complex. One line of sand- 

 hills, starting from the marginal sand ridge of the river, a mile or two 

 south of Havana, and extending in a northeasterly direction for four 

 or five miles, presents some slight evidence of pure wind origin. The 

 long axes of these hills lie in the same direction as the whole range, 

 and the hills are usually about forty feet high and a quarter-mile long. 

 The sand composing them is quite pure. The Devil's Hole is one very 

 sandy part of these dunes. Some of the fields in this region having 

 been plowed up, the blowing immediately became so serious that agri- 

 culture had to be abandoned, and now the sand that is not blowing is 

 reverting to bunch-grass. The bunch-grass is usually pastured. 



The large island between the Illinois and the old channel of the 

 Mackinaw, now occupied by Quiver Creek (see PI. I) presents the 

 surface configuration of a stabilized dune-complex. On this former 

 island, three miles north of Topeka, is the blowsand region known as 

 the Devil's Neck. This is almost entirely under the control of the 

 wind, and has an area of about 80 acres. A triangulation station of 

 the Illinois River Survey of 1905 (PI. Ill, Fig. 2) is situated on one 

 of the highest dunes on the island, about a mile north and east of the 

 Devil's Neck. The top of this dune is seventy feet higher than the 

 trough of a depression not far away, and from the summit an un- 

 interrupted view for miles may be had. 



The drainage line of Crane Creek, extending from the Mackinaw 

 valley through the re-entrant northeast corner of Mason county in a 

 southwest direction to the Sangamon River, marks another of the 

 great channels of the ancient stream. The Black-jack Ditch occupies 

 a third broad flat, extending northward from the Sangamon bottom- 

 land nearly to Havana. Its northern end is drained by White Oak 

 Run, which flows west into Matanzas Lake. The flats of Crane Creek 

 Ditch and the Black-jack Ditch are covered with the sandy loam soil, 

 and until they were used for agriculture were partly swamp, certain 

 spots having been under water almost the year round. The subsoil is 



