MONTANA BUREAU OF MINES AND GEOLOGY MBMG Geologic Map 64; Plate 1 of 1 A Department of Tech of The University of Montana Clinker Distribution and Age in the Powder River Structural Basin, 2013

107°30'0"W 107°0'0"W 106°30'0"W 106°0'0"W 105°30'0"W 105°0'0"W 104°30'0"W 46°30'0"N Clinker Distribution and Age in the Powder O’Fallon Sandstone Cr Little Porcupine Cr 59 z{ I-94 ¨¦§ 3310I# Locate Creek Powder River Structural Basin z{12 Miles City ! z{12 By I# 2502I# 3269 Edward L. Heffern, U.S. Bureau of Land Management (Retired) 3121I# 2941I# Big Porcupine Cr Custer County Pine Cr Rosebud County Tongue River Peter W. Reiners, University of Arizona, Tucson, AZ River

Creek Yellowstone River Catherine A. Riihimaki, Drew University, Madison, NJ I# 2623 Yellowstone River 2013 Moon Cr Sheep Creek ¨¦§I-94 ! Graveyard Cr Sarpy Cr Forsyth Land and Resource Data Rosebud Creek $ 80 Powder Sweeney Cr Lame Jones Cr ! Cities and towns Major paved highways $ 79 T5N 2706 I# State boundary Interstate highways Yellowstone Armell’s Cr County Milk Cr County boundary Rivers and streams T5N

Spring Cr Tullock Cr Fallon County I# 4301 Summit elevations in feet above mean sea level River Carter County z{59 Area underlain by Tertiary sediments Ash Cr East Fork E Fk Armell’s Cr I#3270 Early Quaternary / Late Tertiary gravel terraces (only those in Montana shown) 2.747 +/- 0.220 2.840 +/- 0.161

Ash Cr I#3400 &-&-") 3.226 +/- 0.258 2.637 +/- 0.166 &- 3.518 +/- 0.166 Mizpah Creek 5.067 +/- 0.288 Coalbed Fires 46°0'0"N 3.8 +/- 1.2 Tongue River O’Fallon Cr Active and historical coal fires, identification number indicated. Refer to coal-fire spreadsheet for details, available on the Foster Cr 46°0'0"N Montana Bureau of Mines and Geology website at http://www.mbmg.mtech.edu/. 39 z{ Pumpkin Creek W Fk Armell’s Cr $ 42 Mine fires $ 47 Spoil fires I#3392 Treasure County $ 41 Outcrop fires Big Horn County I# Liscom Cr 3726 Little Beaver Cr The , with its dry climate, low-rank coalbeds rich in volatile matter, and commonly occurring range fires, $ 8 ! I# ! provides ideal conditions for coalbed fires. Near-surface and exposed coalbeds above the water table have ignited due to causes 4462 Colstrip Ekalaka as diverse as lightning strikes, wildfires burning trees and bushes rooted in coalbeds, and spontaneous combustion in coal mines ") 2.2 +/- 0.8 I#") and outcrops. The 81 coal fires shown were compiled by the lead author from personal contacts and observations, published 2.9 +/- 0.9 4807 Tullock Cr Rosebud 3228 Spring Cr maps and articles, U.S. Bureau of Mines fire control project reports, and U.S. Office of Surface Mining, Abandoned T1N $ 9 I# Dry Cr Mine I#3948 Mine Land Division, and U.S. Bureau of Land Management records. The recent vast range fires in the northern Powder River $ 11 I#3764 T1N Basin during the summer of 2012 may have ignited additional coalbed fires. Absaloka $ $ 10 $ 12 Custer County Mine 64 Beaver Cr Rosebud Creek 0.603 +/- 0.028 Powder River County &- Powder River Coal Mines T1S I# 2944 Mined areas through 2010 Little Pumpkin Cr T1S ") &- 0.120 +/- 0.006 Timber Cr < 0.4 &- 0.515 +/- 0.019 &- $ 3583I# 0.217 +/- 0.127 The 16 active coal mines in the Powder River Basin—12 in Wyoming and 4 in Montana—include the largest coal mines in North Rosebud County 13 $ 73 America. These mines produced 462.6 million short tons, 42.2% of total U.S. production, in 2011 (U.S. Energy Information Adminis- 1.1 +/- 0.3 ") $ 71 15 &- 0.326 +/- 0.016 Little Wolf Mountains &- 1.073 +/- 0.086 ") 0.2 +/- 0.1 $ tration). Of this total, 426.1 million short tons came from Wyoming and 36.5 million came from Montana. The approximate areas Little 14 $ B' I# &- 0.652 +/- 0.026 where coal has been mined are shown in dark gray on the map. These areas are based on mine plans and annual reports of coal 4541 0.981 +/- 0.039 &-&- 0.110 +/- 0.009 17 0.105 +/- 0.005 &-") 0.8 +/- 0.2 ") 0.6 +/- 0.6 0.155 +/- 0.009 mine permits on public file with State mine regulatory agencies. Total areas mined through the year 2010 cover about 164 sq. mi. $ &- # Crow Cr 16 $ B I ! 4327 (425 sq. km.). Each mine has a program to quickly extinguish coal fires in mining pits, highwalls, and spoil piles. ! Crow Agency 18 Pumpkin Creek Lame Deer $ ") 1.0 +/- 0.3 Ashland 4407 ") I# $ 0.4 +/- 0.3 ! &- 0.287 +/- 0.023 Cabin Cr Big 19 &- 0.227 +/- 0.013 &- 0.152 +/- 0.012 Clinker Creek &- 0.308 +/- 0.025 212 &- 0.014 +/- 0.002 z{ Mizpah Creek I#4396 20 &- 0.089 +/- 0.013 Clinker outcrops Busby! *# $&- 0.056 +/- 0.004

212 ") Powder River County

Horn Reno Cr z{ 0.9 +/- 0.3 Carter County * 45°30'0"N # Clinker is rock that has been baked, sintered, or melted by burning of underlying coalbeds. Clinker forms reddish layers that cap hills Pilgrim Cr and escarpments in the landscape. In the southeast corner of this map (and Inset Map 2), the Rochelle Hills form an east-facing

") 1.3 +/- 0.3 Otter Creek * # Corral Cr 45°30'0"N escarpment capped by clinker of the Wyodak coal zone. The coal is being mined just west of its outcrop/burn line. Nearly all of the

1.0 +/- 0.4 ") 21 $

Rosebud 22 * # $

") I#4161 coal in the map area occurs in formations of Tertiary age. The clinker in the map area results from natural burning in prehistoric times * 1.5 +/- 0.5 # ¨¦§I-90 ") &- 1.0 +/- 0.4 0.014 +/- 0.005 3304I# of coalbeds in the Paleocene Fort Union and Eocene Wasatch Formations. Additional clinker may be present in the subsurface River < 0.2 ") &- beneath younger alluvium, but not exposed at the surface. Clinker is also common in landslides and talus deposits downslope from 0.237 +/- 0.017 ! clinker-capped ridges. $ Broadus 23

T5S Clinker outcrops shown on this map of the Powder River Basin cover a total of 1,472 sq. mi. (3,812 sq. km.). Of this total, 1,094 sq. I#3648 T5S mi. (2,833 sq. km.) of clinker are in Montana and 378 sq. mi. (979 sq. km.) are in Wyoming. These clinker outcrops represent the R35E Box Elder Cr R40E ") 0.8 +/- 0.4 ") 1.1 +/- 0.4 natural burning of tens of billions of tons of coal. Much additional clinker, perhaps an order of magnitude more, has been eroded ") R45E R55E away and carried downstream into the tributaries of the Missouri River. The record of this eroded clinker is present as clinker cobbles Lodge Grass 0.8 +/- 0.7 Tongue River R50E in Quaternary and late Tertiary gravel terraces. Natural coal fires have been a significant source of greenhouse gas emissions in ! # River I4348 3440I# E Fk Little Powder River prehistoric times, although the rate of natural burning is much less than the current rate of coal mining. I# I#4774 5155 &- 1.113 +/- 0.040 I#3365 The clinker outcrops shown were mapped by E.L. Heffern, the lead author, from the following public sources: published geologic maps Wolf Mountains and digital data files from the U.S. Geological Survey, Montana Bureau of Mines and Geology, and Wyoming State Geological Survey; Lodge Grass Cr I# z{59 3901 data interpreted by the author from color and color infrared aerial photography and National Agriculture Imagery Program color and River # Owl Cr 4301I color infrared orthophotos; and data from coal mine permit maps on public file with the State of Wyoming Land Quality Division. The full reference list is available on the Montana Bureau of Mines and Geology website at http://www.mbmg.mtech.edu/. I# &- 0.127 +/- 0.020 # S Cottonwood Cr 3743 I 4245 The Tertiary bedrock of the Fort Union and Wasatch Formations is mostly poorly to moderately consolidated sandstone, siltstone, Horn z{212 and shale interfingered with coalbeds. When a subaerially exposed coalbed catches fire, the fire front burns back beneath the &- 0.270 +/- 0.021 sandstone, siltstone, and shale overburden of these sediments. It ‘fires’ the overlying rock in a manner similar to ‘firing’ bricks. The Big 72 result is the hardened, fractured rock called clinker. Most clinker is red, but some contains shades of yellow, orange, and black. In $ I#3490 Spring &- general, baked sandstone retains its original grain structure. The grains of fine-grained sediments are sintered—heated and welded Ross Cr 0.239 +/- 0.015 24 Creek $ together to form a coherent mass without melting—resulting in a rock similar to porcelain. A small amount of rock—primarily in Little Willow Cr fissures that served as chimneys— has been melted to hard black paralava. Virtually all of this clinker is harder than the parent rock. Mine Tongue River Reservoir Powder At the base of the clinker lies a thin layer of light tan ash mixed with greenish glass. In addition, clinker is highly fractured and allows I#4450 $81 much water to drain through rather than run off. The greater hardness, combined with fracture permeability, makes the clinker more West Decker &- 0.013 +/- 0.001 58 63 5444I# resistant to erosion than the unfired bedrock strata above and below. Consequently, regional downwasting leaves the clinker forming $ $ 59 $ 3731 T9S Mine $ I# 62 the tops of scarps and ridges. See block diagram and cross sections. East Decker $ 66 $ River Cr R35E 60 T9S R40E 3970 $ 61 45°0'0"N &-&- Mine I# &-&-&- River R45E &-&- &- R50E &-&- Montana R55E &- &- 45°0'0"N &- Badger See Inset Map 1 &- Tongue Wyoming &- 42 $ Thompson &- 41 Cr Bitter $ Cr 43$ 44 77 $ Dry I#4011 $ Olmstead River $ 78 $ 27 Cr $ S A Cr Cr 45 $ $$ 48 $ 29 R

46 Dog $ 30 3757 R85W 47 L X Bar I# 52 Cr MissouriR65W 33 Powder North Fork Little I# R80W R75W 31 R70W 8305 Goose 32 Tongue River Cr $ Missouri Cr $$ Dutch 14 $ 40 34 z{ $ 28 $ Wolf Prairie z{59 T55N $ Cr Cr Cr Spotted Little 35 Duck T55N Sheridan! Buffalo I# $ T55N River Horse 53 Cr Cr 4002 Little Goose Cr

Big Little &- 0.096 +/- 0.004 Prairie Cr &- 70 0.225 +/- 0.028 $ $ Powder 65 z{14-16 Cr Missouri Block diagram of clinker-dominated landscape (from Heffern and Coates, 1997) 39 $ 36 0.205 +/- 0.009 $ Hulett ! Cr 0.095 +/- 0.029 &-&-&- Horse 0.108 +/- 0.005 $ 37 Cr

14 $ 38 z{ R Goose 76 $ &- $ 51 4636 I# 0.013 +/- 0.010 Sheridan County I#4470 0.077 +/- 0.017 Campbell County &- &- I# 0.211 +/- 0.012 I#10828 4886 Clear Creek Wildcat Devils Tower Piney Cr 5110I# Sheridan County Wild 4921 ft I# R 9358 Johnson County Cottonwood Belle Fourche River Powder Bear Lodge Horse &- Little 0 2 4 miles 4593 ft 44°30'0"N 0.019 +/- 0.001 Boxelder Cr Mountains 56$ Cabin Cr Miller Cr $ 50 7 44°30'0"N 0.012 +/- 0.017 &- &- 0.114 +/- 0.005 Cr $ 0.133 +/- 0.006 0.016 +/- 0.097 0.018 +/- 0.012 16 &-&- &- 0.188 +/- 0.011 &- z{ Buckskin 0.105 +/- 0.005 0.191 +/- 0.008 Lake DeSmet &- Fortification $ Cr 49 Mine I#4672 0.018 +/- 0.004 Schematic cross section A–A', Rochelle Hills, east of Wright, WY Rock Cr River $ 68 Inyan Kara 5130I# Cr River $ 1 Crook County Cloud Peak 67 Rawhide I# $ 75 Campbell County T50N 13167 $ Mine #* $ Arch 55 T50N Keyhole Reservoir T50N 3937 ft 0.117 +/- 0.007 &- 0.024 +/- 0.010 &- Eagle Butte Cr Buffalo &- ! 0.031 +/- 0.006 Mine 0.227 Cr Barber Dry Fork Mine +/- 0.013 Clear Creek I#4835 Cr 0.183 +/- 0.008 Keyhole Reservoir 0.042 +/- 0.002&-&- 3281 ft $ 54 Wind 0 5 mi

Powder I-90 River ¨¦§ 4262 ! Donkey I# 0 5 km Wyodak Cr Woman Cr Gillette Mine $ $ 26 Dead 16 I-90 Horse 3 z{ North ¨¦§ Cr Schematic cross section B–B', Tongue River Valley, near Ashland, MT Big Horn County Fork Buffalo Fourche Crook County Washakie County Cross section clinker of Knobloch coal zone Weston County clinker of Anderson coal zone Caballo Mine Ma = millions of years Belle Cr clinker of other coal beds Crazy Crazy Belle I#4586 Ayr Beaver Mine 16 I#10534 I#5204 Four Horse Raven z{ (Cross sections from Heffern and others, 2007) Cr 0.013 +/- 0.002 Caballo Tensleep Cr Cr &- Woman Cr Middle Flying E Cr Fork Age of Clinker 59 Cr How long ago did coal at a given location burn to form clinker? Clinker can be dated by several means, including uranium-thorium / z{Cordero- Pumpkin 44°0'0"N Rojo helium ratios and fission-track counts in zircon grains from within baked sandstone, as well as paleomagnetic dating of magnetite, Mine 6 $ hematite, and goethite in paralava. These dates, in turn, help us to better understand how the landscape evolved over geologic time South Fork 44°0'0"N as major river systems cut down into the sediment of the Powder River Basin, and the rate at which coalbeds were exposed, burned, Cr and released combustion gases into the atmosphere.

T45N ¨¦§I-25 T45N Wild Horse Cr Coal Creek T45N Uranium-Thorium/Helium (ZHe) ages of clinker, in millions of years (Ma)

North I# Mine 7723 River 4991I# &- 0–0.049 &- 0.500–0.999 Ninemile Cr River Johnson County Washakie County Washakie Dry Willow &- 0.050–0.149 &- 1.000–1.999 Fork &- 0.150–0.249 &- 2.000 and older &- Powder River 0.250–0.499 Cr ") < 0.3 Fourche Mud Spring All ZHe analyses are from Reiners and others (2011), Riihimaki and others (2009), and Heffern and others (2007). Powder ") < 0.3

Nowood River

Belle ") 0.9 +/- 0.6 Cottonwood I#6049 Hay Zircon fission-track (ZFT) ages of clinker, in millions of years (Ma) Red Fork ") 0–0.149 ") 0.500–0.999 Fourmile Pumpkin Buttes Cr Powder River Wright ! see Inset Map 2 ") 0.150–0.249 ") 1.000–1.999 Cr Jacobs Kaycee Cr Ranch Black ") 0.250–0.499 ") 2.000 and older ! Mine ") Lodgepole ") ") ") ") ")") ") All ZFt analyses are from Heffern and others (2007) and Coates and Naeser (1984). River $ ")&-#*") 2 ") ") Thunder 0.024 +/- 0.001 &- &-") ") R85W Powder &- R80W R75W R70W Little R65W Cr Paleomagnetic samples of clinker Thunder Cr

&- *#

Black Thunder Cr Normal polarity

* Fork Porcupine Mine Rochelle # ") Reversed polarity Middle Salt Cr Hills All paleomagnetic analyses are from Jones and others (1984). I#8318 Cr Meadow z{387 &- Normal polarity indicates the coal burned more recently than the Matuyama-Brunhes magnetic reversal at about 0.78 Ma. Cr A &- Cr I# &- River &-") &- 5307 &- A' Cr North Antelope/ &- &- Bates R36E R37E 43°30'0"N Rochelle Mine I# T40N $ 4

5175 T9S Johnson County Dugout 0.565 +/- 0 019 T40N T40N Cheyenne River 0.924 +/- 0.244 Campbell County Cr Weston County 43°30'0"N &- &- Cr MT . &- Natrona County Antelope 0.802 +/- 0.029 Buffalo Converse County #* Niobrara County &- Mine Antelope WY 0.648 +/- 0.023 &- #* 0.202 +/- 0.030 &- T10S Antelope #* &- 0.301 +/- 0.045 Powder &- Willow Cr &- 1.009 +/- 0.073 &- Cr &- &- 0.352 +/- 0.027 &- 0.498 +/- 0.051 Bighorn Mountains &- 0.396 +/- 0.032 0.456 +/- 0.075 &- Salt $ 5 &- Sand Cr 0.578 +/- 0.080 &- &- 0.334 +/- 0.132 Cr Fork *##* T57N T9S Cr &- Castle $ 1 Mile 0.275 +/- 0.120 25 $ 0.562 +/- 0.034&- 69 Cr 1 Km South Cheyenne River Cottonwood Indian Cr 59 I#4892 Teapot z{ Dry Fork 0.130 +/- 0.022 &- Cr T56N Inset Map 1 0.242 +/- 0.069 &- Dry Cr R85W R84W R83W Cr Niobrara County Converse County Lightning R70W R69W R68W R67W

Cr

T43N Inset Map 2 $ 74 Cr Jacobs Ranch Mine I# 5370 Box

T35N North Lance ") < 0.6 ")< 0.5 ") 0.4 +/- 0.2 0.3 +/- 0.2 Powder River Fork Cr Cr < 0.09 ") 0.3 +/- 0.3 ") ")") 0.7 +/- 0.3 T35N ") 0.5 +/- 0.4 &-*#")0.536 +/- 0.025 I# 6090 T35N ")*# 0.7 +/- 0.3 ") 0.8 +/- 0.5 Walker 0.5 +/- 0.3 Lightning T42N ") 20 Casper Cr 0.4 +/- 0.2 South Fork z{ Cr R70W 0.3 +/- 0.2 ") ") Fork 0.198 +/- 0.011&- &- 0.5 +/- 0.3 43°0'0"N Dave Black Thunder Mine 0.482 +/- 0.027 Casper Johnston Cr Middle Mine 43°0'0"N &- Sage Twentymile 0.127 +/- 0.010 Cole Cr 5645 I# Wallace Cr Casper Cr Sand ") < 0.5 6064 I# Cr

South Fork T41N 5303 Soda Lake I#

Cr &-0.205 +/- 0.012 0.010 +/- 0.001 A &- &- Platte River 0.502 +/- 0.028 Spider North Antelope / Rochelle Mine 0.120 +/- 0.008 &-") &-&- 0.615 +/- 0.035 Poison North &- Cr ! ¨¦§I-25 0.219 +/- 0.009 0.7 +/- 0.4 0.550 +/- 0.031 Casper &- A' Cr &- R85W Cr R65W 0.211 +/- 0.012 0.216 +/- 0.012 R80W North Platte River R75W Cr R70W 220 z{ Deer T40N Cr Muddy Douglas Antelope Mine ! z{18 LaPrele *# I#7414 Laramie Mountains Cr Cr Box Elder I# *# 5717 &-0.213 +/- 0.012 Lost *#

T30N I# 487 8255 &- 0.007 +/- 0.006 z{ Shawnee &- T30N T30N 0.115 +/- 0.008 0.249 +/- 0.023 107°0'0"W 106°30'0"W 106°0'0"W 105°30'0"W 105°0'0"W &- 0.096 +/- 0.006 Base map created in ArcMap for a poster presentation at AAPG Transverse Mercator Projection T39N 10 Miles Rocky Mountain Section Meeting, Cheyenne, Wyoming June 2011. 10 0 10 20 30 40 miles UTM Zone 13N, NAD 1983

0.016 +/- 0.006 &- 10 Kilometers 10 0 10 20 30 40 50 kilometers

This map prepared in cooperation with the U.S. Bureau of Land Management.

No warranty is made by the Bureau of Land Management as to the accuracy, reliability, or completeness of these data for individual use or aggregate use with other data.

Published by the Montana Bureau of Mines and Geology

The authors thank Stefan Nicolescu, Victor Valencia, and George Gehrels for analytical assistance on dating the ZHe samples; Jason MBMG Whiteman, William Reiners, Paul Gore, Zoe Ruge, Camille Jones, Jessica Scheick, and Kaia Davis for field assistance in sample Ed Heffern below the base of the clinker formed by Mark Engle of the U.S. Geological Survey sampling gases coming View of collapse along burn front of the same active coalbed fire shown in collection; Don Luse for access to the Padlock Ranch; Donald Coates, the burning of the Knobloch coalbed in the Tongue off a coalbed fire along the banks of the Tongue River north of picture to left, north of Sheridan, Wyoming. The reddish color in parts of the Maps may be obtained from: River valley north of Ashland, Montana. Collapsed Sheridan, Wyoming. collapsed area marks areas where clinker has formed. Publications Office Charles Naeser, and Roger Colton of the U.S. Geological Survey A 25-foot high chimney of hard, welded breccia and paralava formed by the The Rochelle Hills escarpment capped by the clinker formed by the blocks of reddish baked sandstone overlie the basal Montana Bureau of Mines and Geology (retired), for their geological advice and expertise; and Larry natural burning of the Wyodak coalbed in the Rochelle Hills, Wyoming. burning of the Wyodak coalbed, at Keyton Canyon east of Wright, ash zone that marks the original base of the 1300 West Park Street Neasloney of the U.S. Bureau of Land Management for Geographic Note the person (white oval) standing on the right side of the chimney. Wyoming. Butte, Montana 59701-8997 Information System advice. coalbed, underneath which is unburned sandstone. Phone: (406) 496-4167 Fax: (406) 496-4451 http://www.mbmg.mtech.edu Layout by Susan Smith, MBMG. Edited by Susan Barth, MBMG.