PERMFILE119279

• Permit No: C1984065
• IBM Index Class Name: Permit File
• Doc Date: 12/11/2001
• Section_Exhibit Name: 3.3 Hydrology and Geology
• Media Type: D
• Archive: No

shale sequence, and the Rollins sandstone, (2) the Bowie
(coal-bearing) member, (3) the Paonia (coal-bearing) member, and •
(4) the Upper (non-coal-bearing) member. The Corcoran and Rollins
sandstones are the bottom and top, respectively, of the Iles
Formation, and the upper three members belong to the Williams Fork
Formation (Figure 3.3-3).
The Iles Formation
The contact between the Mancos shale and the Iles Formation has
been defined differently by several researchers. One group defines
the bottom of the Iles Formation as the bottom of the Rollins
sandstone, whereas another group defines the contact as the bottom
of the first significant sandstone near the top of the Mancos
shale, which in this area is the Corcoran sandstone. There have
been several other attempts to define the contact, but these two
approaches represent the most viable. With respect to this report,
the resolution of this controversy is not critical, however,
practical considerations require a contact between the two forma- •
tions. Because the Corcoran sandstone is more mappable on aerial
photographs, it was used as the Mancos-Iles contact in the area of
concern.
The Iles Formation is 1060 feet thick near South Canyon and 970
feet thick near New Castle. in ascending order, the Iles Formation
is composed of the Corcoran sandstone 130 feet thick, a shale-sand-
stone sequence 725 feet thick, and the Rollins sandstone which is
80 to 120 feet thick.
The Rollins sandstone consists of fine to medium-grained feld-
spathic, grayish-white sandstone that weathers to light buff.
Bedding is commonly massive, but local variations occur. The
Rollins sandstone is an important marker horizon throughout the
region since it is everywhere directly overlain by the principal
coal-bearing zone of the Williams Fork Formation (Collins, 1976).

FCSC - Coal Ridge #1 3-12 ]18C/1145/900301