444 SUPPLEMENTARY INVESTIGATIONS IN THE GRAVEL REGION. 
Downieville and Indian Hill, I did not explore at all; but it seems highly probable that the 
remarkable boulder stratum at the latter place was once in easy communication with such deposits 
as that at Loganville. The boulders, at least, may well have had the same origin. Over some 
portions of this district of country it is hard to tell where volcanic or plutonic agencies ceased to 
act, and glacial or fluviatile began. 
Section VII. — Zhe Region North of the North Yuba River, and South of the Divide 
between the Yuba and the Feather Rivers. 
This extensive and important district lies partly in Sierra and partly in Plumas County. The 
boundary of the portion to be referred to in this report follows the ridge to the west of Slate 
Creek and La Porte as far as Pilot Peak, thence along the high erest, to the headwaters of the 
North Fork of the North Yuba River, and finally down the North Fork and the North Yuba, by 
way of Downieville, to the point of beginning. 
There is no published map of the whole of this region to which the reader can be referred ; 
none, that is, on a sufficiently large scale. At the court-house in Quincy, the county seat of 
Plumas County, there is a map in manuscript entitled ‘‘ Official Map of Plumas County. By 
Arthur W. Keddie, C. E. Based on the work of the State Geological Survey by V. Wacken- 
reuder, in 1866, under the direction of J. D. Whitney, State Geologist. Approved by Board of 
Supervisors, May 6, 1874. T. B. Whiting, Clerk of Board.” From a tracing of this map in 
Mr. Hendel’s office at La Porte, to which he had made additions from his own surveys, I made a 
second tracing of such portions as were necessary for the work in hand. ‘The scale of this tracing 
is a mile and a half to one inch. Mr. Hendel also kindly allowed me to make use of data, which 
he had collected in his surveys, in the preparation of maps of parts of this district, to which refer- 
ence will be made on subsequent pages. 
The principal topographical features of this district are very striking and well-marked. The 
lowest point is at its southwestern corner, in the canon of the North Yuba, where the altitude 
is not far from 2,000 feet. The highest peak is Alturas Mountain, near Howland Flat, of © 
which the altitude — not precisely determined — is probably over 7,500 feet. The caions, which 
have a general southwesterly direction, are deep and narrow ; and the intervening ridges are also 
narrow and sharp. A line drawn in a southeasterly direction from a point near La Porte crosses, 
within a distance of less than twelve miles, four deep caiions, — those of Slate, Caiion, Little 
~ Caiion, and Goodyear creeks. The trail from La Porte to Downieville crosses the ridge between 
Slate Creek and Caiion Creek at an altitude of more than 1,000 feet above the stream on either 
side. Between Caiion Creek and Little Cafion Creek the trail by way of Craig’s Flat reaches a 
height of 800 feet above the level of the water ; and a ridge nearly a thousand feet high has to be 
crossed in getting from Little Cafion Creek to Goodyear Creek. Beyond Goodyear Creek the sag 
in the ridge at Monte Cristo is still higher. The relative positions and altitudes of several points 
on the Downieville trail are given on the diagram section. (Plate G, Fig. 3.) There are a few 
good wagon-roads in the western part of the district, connecting places on the opposite sides of 
Slate Creek ; but, for the rest, the chief dependence has to be placed on trails. The extreme irregu- 
larity of the surface and the lack of easy means of communication make it difficult to get anything 
more than a general outline of the geological structure without the expenditure of a great deal 
of time. 
The prevailing bed-rock is a slate, similar in character to that which makes up the greater part of 
the western slope of the Sierra Nevada. Its local variations and modifications will be referred to. in 
the descriptions, which are to follow, of special localities. The slate is crossed by a belt of serpen- 
tine, which follows a course a little to the west of north, and which has in places a width of at 
least four or five hundred feet. I cannot say whether this belt is a continuation of that which has 
already been referred to as crossing the Forest City divide, or is a separate belt, nearly parallel with 
the former. At present I am inclined to the latter opinion, for the Forest City serpentine, unless 
