12 FAIRBANKS AND RAMPART QUADRANGLES. 
lines and crescent-shaped areas of water indicate the many inter- 
lacing channels of the Yukon which are spread widely over this great 
flat: The lowlands of the southern border, the Tolovana and Baker 
flats, are embayments from a similar great flat that forms a large part 
of Tanana Valley. 
The main features of the surface can be learned from the topo- 
graphic maps and need no further comment in the text. The relief, 
the drainage, the relations of the various drainage systems to each 
other, the grades of the streams, the comparative elevations and 
grades of different valleys are all brought out on the maps, and many 
of their economic relations are thus made clear to those who read the 
maps with care. If, for example,- the digging of a ditch or the con- 
struction of roads or railways is under consideration, the most feasi- 
ble routes can be approximately determined by a study of the maps. 
The explanation of the uniformities in altitudes is to be found in 
the history of the region. The ridge level is a remnant of a former 
continuous more or less uniform surface tying at a lower altitude 
near sea level. Subsequent elevation has resulted in the cutting of 
the present valleys. The explanation of local differences of relief, 
like that of Pedro Dome with its surroundings or the White Moun- 
tains in the Fairbanks region, or Wolverine Mountain in the Rampart 
region, is to be found largely in differences in the character of the 
bed rock that are accentuated under the conditions of the present 
downcutting. The local granitic intrusives in Pedro Dome and 
Wolverine Mountain have withstood erosion and held up these 
areas, and the limestone of the White Mountains performs the same 
function. 
Stream adjustments are also clearly shown on the map. An ex- 
ample may be taken from the Beaver Creek system. One of the 
small tributaries draining the southern part of the White Mountains 
has been called, for purposes of description, Fossil Creek, from the 
occurrence of fossiliferous limestone pebbles in the gravels. East of 
the single narrow limestone ridge that terminates the White Moun- 
tains is a parallel ridge of shorter extent. Between the two lies a 
low-grade valley, 2 miles wide, extending northeastward for nearly 
10 miles and drained by a stream that flows along its western side 
close to the base of the limestone ridge. From the base of the ridge 
on the east, broad, flat spurs, separated by open depressions so shallow 
as to be hardly noticeable, extend westward to the stream. On close 
examination the apparently continuous valley is seen to be composed 
of two parts — a lower, drained by a stream which seems dispropor- 
tionately small for the size of the valley and which has its rise in a 
few small stagnant ponds strung longitudinally along its course 
about 5 miles from Beaver Creek, and an upper, drained by a stream 
of about the same length, which flows at first southwestward, in line 
