This document is a geologic map of the Block Mountain area showing various rock units and structural features. The map contains elevation data along two cross-sections (A-A' and B-B') and labels numerous rock units with symbols and abbreviations. Accompanying the map is a legend that provides brief descriptions of each rock unit, including their typical lithology, thickness, bedding, and whether they form cliffs or slopes. Structural features like thrust faults, anticlines, and synclines are also indicated on the map.

1. 0 4000 6000 8000 10000 12000 14000 160002000
4593
2624
3280
3937
5249
18000
A A’
Trd
Trd
Kka
Kka Kka
Kkb
Kkb
Kkb
Kkc
Kkc
KkcKkd
Kkd
Tkb
Ki
Kbfl
Kbfl
Kbfu
KbvPp
Pp
PPq
PPq
PPq
2000 4000 6000 180001600014000120008000 10000
1312
2624
3937
5741
1968
3280
4593
5250
0
B B’
Trd
Trd
Kka
Kka
Kkb
Kkb
Kkc Kkc
Kkd
Tkb
KbflKbfl
Kbfu
Kbv
Pp
Pp
PPq
PPq
¯
Block Mountain Area Geologic Map
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68
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17
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70
4565
60
41
45
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Kkc
Kka
Trd
Kbv
Trd
Pp
Kkd
Pp
Kkb Kkc
Kbfl
Ki
Kkb
Kkb
Kbfu
Kkc
Kkd
Kkb
Kkd
Kkc
PPq
Kbfl
KkaPp
Kkb
Kkc TkbKkaKkb
Kbfu
Kbfu
38
10
59
60
28
20
45
50
56
75
41
70
17
52
25
33
70
65
65
62
30
25
35
21
12
65
38
35 55
40
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50 4547 43
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45 30
58
37 46
65
71
61
35
80 40 42 25
50
63
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320
0 1 20.5 Miles
B
B‘
A
A’
Unit Descriptions
Quaternary Alluvium: The North-East corner of the map contains an extensive alluvium de-
posit including granite and hornfels alluvium. This alluvium forms a fan like ridge which cuts
through the Kootenai members.
Tertiary Basalts: The Tertiary Basalts are dark gray to black porphyritic basalt rich in olivine
phenocrysts with fewer plagioclase phenocrysts. This unit forms the bench that is Block Mountain as
well as a dike which cuts through the Sandy Hollow Anticline.
Andesite Sill: This unit is a dark gray to green porphyritic andesite containing plagioclase
phenocrysts. The unit is found in the western portion of the map area and tends to follow the gener-
al trend of the Creasey Gulch Anticline.
Vaughn Member of the Blackleaf Formation: The Vaughn Member of the Blackleaf formation,
present in the study area, consists of a light green to gray porcelanite. This unit is a medium bedded
slope former which is highly fractured.
Upper clastic unit of the Flood Member of the Blackleaf Formation: The Upper clastic is a lav-
ender to light red feldspathic litharenite. The sandstone is thickly bedded, well cemented, coarse
grained, and forms a cliff. It is parallel laminated, with small amounts of cross bedding. Near the base
of the unit there is some thinly interbedded medium grained sand, silt, and mud.
Middle shale unit and lower clastic unit of the Flood Member of the Blackleaf Formation: This
unit contains a black shale interbedded with a gray to tan, calcareous, litharenite sandstone. The li-
tharenite is thin to medium bedded, trough cross bedded, and can form either slopes or cliffs. Near
the base of the unit there is a coarsening upward succession with a fairly thick sandstone near the
middle. Overlying the sandstone is a thick layer of shale which reaches the base of the upper clastic
unit. This unit forms both cliffs and slopes.
Kootenai D Member of the Kootenai Formation: The Kkd is a dark gray to light gray gastro-
pod bearing wackestone or packstone. The unit is a thickly bedded, prominent cliff former and is 90
feet thick in the research area.
Kootenai C Member of the Kootenai Formation: The Kkc contains a red, brown, or light gray
siltstone to mudstone and a litharenite sandstone. It is primarily, thinly bedded, but is also medium
to thickly bedded in some localities. The sandstone contains a high degree of cross bedding as well
as lenticular structures. It is moderately cemented, medium to coarse grained, and can contain
pebble sized clasts. This unit can be expressed as either a cliff former or slope former.
Kootenai B Member of the Kootenai Formation: The Kkb contains a light to dark gray fossilif-
erous lime mudstone to wackestone. The mudstone/wackestone is medium to thickly bedded and
forms prominent outcrops. The fossils in this layer consist mostly of disarticulated gastropods. The
Kkb also conatins a yellow, tan, to orange dolostone unit, near the base, that is dark gray and crystal-
line on a fresh surface. The dolomite is medium bedded and typically forms slopes. The entire Kkb is
175 feet thick.
Kootenai A Member of the Kootenai Formation: The Kka contains a brown polymictic cobble
to gravel orthoconglomerate near the base. The clasts are comprised of quartzite, chert, and lithics.
The conglomerate is overlain by a tan to gray, coarse grained, litharenite sandstone. The litharenite is
medium bedded, contains trough cross bedding, lenticular bedding, and may contain gravel sized
clasts. It is interbedded with a red to green, thinly bedded claystone that forms slopes in outcrop.
The orthoconglomerate and litharenite form prominent outcrops although they are both discontin-
uous units. The Kka is 455 feet thick.
Dinwoody Formation: The Dinwwody Formation contains a brown to light gray dolomitic
lime mudstone, and dolomitic wackestone. The Dinwoody Formation also contains a thinly bedded
calcareous siltstone that contains brachiopod fossils. The Dinwoody is thin to medium bedded and
can form either slopes or cliffs. The beds within the Dinwoody are often highly folded and contain
slickensides.
Phosphoria Formation: The Phosphoria Formation consists of a thinly bedded blue chert unit
overlain by a brown thinly bedded litharenite sandstone. The sandstone is well cemented, medium
grained, and massive. The Phosphoria is found in the middle of the map area along the thrust fault,
and contains duplexes where it is exposed on Burma Road.
Quadrant Formation: The Quadrant Formation is an orange to white, well cemented Quartza-
renite. The Quadrant’s bedding surfaces are difficult to distinguish from cleavage, fracture, and bed-
ding surfaces, it contains a high degree of slickensides, and it forms large prominent outcrops. The
Quadrant is exposed in the South central portion of the map along the Burma Road.
By Zeb Teichert
Cross Section Units in Feet
Qal
Tkb
Ki
Kbv
Kbfu
Kbfl
Kkd
Kkc
Kkb
Kka
Trd
Pp
PPq
Thrust Fault
Strike and Dip Symbol
Anticline Symbol
Syncline Symbol
Contact Certain
Contact Uncertain
Scale1:12,000