Durango semi-weekly herald., 1902-01-27
COLORADO
OIL STRATA
Second Part of an Instructive
Report, Referring to the
Northern Part.
Instructive in the Comparison
With the Facts Relating
to South Part.

From Archuleta County we now
proceed to the northwest corner oi
the state to Rio Blanco and Routt
counties, and to the region of the
great Book Cliffs. Here we find a
vast body of sedimentary strata
piled up into plateau over 1000
feet in height and extending in
length over 100 miles, and in width
over 80 miles. This plateau CON
sists of about 1000 or 5000 feet oil
Tertiary rocks resting upon Creta.
ceous rocks below, including the
Laramie and Upper Montana Groups.
This is part of vast, low westerly
dipping, anticlinal. whose main axis
is In the Uncompaghre Plateau west
of the Grand river where the arch
of Red Trias rests directly on the
granite, and from this axis the later
beds of the Jurassic and Cretaceous
dip off in rotation in a general west
erly and northwesterly direction.
In the Book Cliffs the oil occur
renee is located in brown sandstones
at the top of thick series of varie-
gated violet color, red, green, brown,
and gray shales and sandstones, that
torn the Wasatch Tertiary. This
series rests directly on the gently
upturned sandstones of the Laramie
coal-bearing' Cretaceous. The oil
spring issues from local fault in
this variegated series, saturating
the surrounding sand stones and
trickling on top of little spring OF
water down over the rocks into the
ravine below. The sands at the
bottom of this ravine are saturated
for distance of several hundred
yards and to an unknown depth
with oil, showing that the spring has
been in existence and has issued
, the same or greater power than to-
day. for a long period of time. The
dripping oil has been temporarily
collected or arrested In rude
wooden tank 6 feet square and deep.
thrown across ravine. In this
? there is probably some or more feet
of crude green oil.
An interesting feature here is the
occurrence of bed about a foot
thick composed almost entirely OF
shells apparently of fresh or
brackish origin. If organic remains
have anything to do with the origin
of oil the presence of this belt of
shell limestone is significant An
other feature in the pale, white and
greenish strata of the Green
River Tertiary rocks everything the
variegated Wasatch Group are beds
of pisolitic or oolitic limestone in
great quantity. Large concretions
of clay ironstone also occur. Many
of the shales of the upper series
are of pale. sea-green color as if
from silicate of iron or glauconite
They appear to carry few iadistinc.
remains of plants or other terres-
trial vegetation.
The Wasatch Green River Tertiary
is generally understood to represent
the deposits of vast fresh-water
lakes. Nearly all the strata are
highly alkaline, and drinking water
for man or beast is scarce We
have only visited one oil spring in
this vicinity, viz. that on Whisky
Creek, but have heard of another 20
miles south of it. Both appear to be
located on the same horizon, viz. at
the top of the variegated series of
the Wasatch Beds. The alienation
of shales and porous sandstones in
these Book Cliffs is favorable for
saturation by oil and forming oil
sands when oil is present. 1t is
notable that the oil spring occurs in
a line of local faulting. so that the
real source of the oil may be lower
than where 1t is found on the sur
face.
From the northwest portion Of the
Book Cliffs we turn east to the ex-
treme eastern limit of this remark
&able formation where the Tertiary
fbeds end abruptly against the high
iy tilted sandstone of the Laramie
Cretaceous. and appear tilted up con
formally with these underlying
strata at steep angle, but In dis
tance of few thousand feet assume
a gradually lessening dip of 10 to 2t
degrees and to the west or south
west. Here are much the same con
ditions as we have described to the
northwest.
The Book Cliff Plateau is surroun
ded by cliffs from 900 to 1000 feet
Sn heighth. of white chalky sand