Black Gold on the Musselshell:

The Rise, Peak, and Long Decline of Montana’s Cat Creek Oilfield

Background: The Land and Its People Before the Drill

The terrain that would one day constitute Petroleum County, Montana, offered little to recommend it to casual observers. Lying in the broad, semi-arid basin between the Musselshell and Missouri Rivers in central Montana, the region was a topographic patchwork of grass-covered gravel benches, sagebrush-choked plains, sandstone rimrocks, and broken badlands. Cat Creek Basin itself measured roughly six miles long and four miles wide, encompassing approximately 16,000 acres at an average elevation near 2,900 feet.  For centuries before Euro-American settlement, Crow, Blackfoot, Nez Perce, and Sioux peoples moved through these lands, hunting and trapping along the river drainages. By 1868, a trading post had been established at the mouth of the Musselshell River, and ranchers began filtering in through the 1870s and 1880s. 

By the turn of the twentieth century, a small but steady stream of homesteaders began claiming land in what would later become Petroleum County, drawn by new farming machinery, favorable land policies, and aggressive promotional campaigns. From 1909 to 1923, approximately 114,620 homestead claims were filed across Montana, and some two thousand of those were on property that would eventually fall within Petroleum County’s boundaries.  These homesteaders found a hard land that had already signaled, to those with eyes to read it, the possibility of something remarkable beneath the surface.

Petroleum indications in the Musselshell country had been noted for decades before any serious commercial exploration began. As early as 1855, a party of emigrants led by William Aldridge, heading northward, spotted oil seepages at Soap Creek and at the Musselshell crossing. In May 1880, cattleman Granville Stuart, scouting the Musselshell River area for new grazing range, noted that petroleum indications ran through the entire region, though he judged the resource commercially worthless at the time.  His assessment was economically accurate for that era, but the geology he was observing would prove consequential forty years later.

Geological Foundations: Reading the Anticline

The structural key to Cat Creek’s eventual productivity lay in what geologists call an anticline, a fold of rock strata in which the layers arch upward, creating conditions favorable to the accumulation of petroleum. The Cat Creek field was examined in a reconnaissance survey for coal by C. F. Bowen of the United States Geological Survey during the summer of 1912. While Bowen did not regard the area as warranting a dedicated oil report at the time, his geological map depicted the distinctive V-shaped sandstone outcrop that would later prove central to the field’s identification and development. 

The structural story of Cat Creek reaches far deeper than Bowen’s surface observations. The Cat Creek anticline is underlain by a south-dipping high-angle fault that has undergone several episodes of movement with opposite senses of displacement. Borehole data suggest the Cat Creek fault originated as a normal fault during Proterozoic rifting concurrent with deposition of the Belt Supergroup, with subsequent reverse faulting episodes in Late Cambrian time and again near the end of the Devonian Period. During the Laramide orogeny of latest Cretaceous to Eocene age, the Cat Creek fault underwent as much as 4,000 feet of reverse displacement.  This complex tectonic history created the structural trap that eventually held the petroleum reserves waiting to be tapped in the twentieth century.

Subsequent research identified the Cat Creek field as one of the oldest and most prolific in Montana, but also noted that the physical characteristics of the crude, its method of entrapment, and its stratigraphic position were anomalous compared to many other fields.  The oil sat at remarkably shallow depths, a characteristic that would make its extraction comparatively inexpensive and straightforward once the field was opened.

Discovery and Development: The Frantz Corporation and the First Wells

The commercial development of Cat Creek owed much to a figure whose biography traced the outer boundaries of American ambition at the turn of the century. Frank Frantz had served as a Rough Rider with Theodore Roosevelt, later served as the last governor of Oklahoma Territory, and eventually turned his considerable energies toward oil exploration through his Denver-based Frantz Corporation. His company found the high-quality crude at extremely shallow depths in the Cat Creek field east of Winnett, a combination of easy access and oil that yielded approximately fifty percent gasoline, making the venture remarkably profitable. 

In late 1919, near Winnett, Montana, the Frantz Corporation began oil exploration on a creek flowing into the Musselshell River, and on February 19, 1920, the company drilled the well that established Cat Creek as Montana’s first commercially productive oil field.  The discovery well, named Antelope No. 1, had shown oil as early as November 1919. Located at the West Dome of the Cat Creek field in eastern Fergus County, it penetrated to a depth of 1,015 feet and produced oil considered by contemporaries to be of the highest grade known in any oil field. 

The opening weeks of production created a logistical problem that offers a revealing glimpse into the unplanned, improvised character of the initial development. John S. “Curley” Meek, one of the first drillers in the Cat Creek area, later recalled that there was no place to store the oil, so it was dammed up in a coulee and given away to ranchers and farmers as sheep and cow dip until they began using it in their cars. According to the Petroleum County Public Library’s county history, Pages of Time: A History of Petroleum County, Montana, with no storage facilities available, oil flowed into a coulee where people from across the countryside came to see it. The crude was of such high gravity it could be used directly in tractors and even Model T automobiles, and it was distributed free of charge to all comers. Storage tanks were quickly constructed, and during the summer of 1920, the Frantz Corporation laid a two-inch pipeline to carry the oil the twenty-two miles to Winnett. 

The Boom Years: Infrastructure, Population, and Corporate Activity

The year 1920 brought a rapid intensification of activity. By May 1920, production from a single well drilled to 660 feet had reached 200 barrels per day. In April 1921, thirty producing wells owned by six different companies were operating at Cat Creek. As many as 300 men lived in the area in tar paper shacks for families, while single men occupied company bunkhouses, with a company cookhouse and recreation hall rounding out the settlement’s amenities. In the town that grew up around the operations, a post office, a church, a school, and a cemetery constituted the full range of public services. 

By the end of 1921, sixty companies were drilling in the Cat Creek area, compared to just six at the start of the year.  The four-inch pipeline eventually constructed by the Midwest Refining Company carried oil to Winnett’s railhead, from which it moved by rail to refineries in Casper and Greybull, Wyoming. Winnett, previously a modest ranching supply town, found itself transformed almost overnight. The town’s population climbed from 1,213 in April 1922 to over 2,000 in 1923. Buildings could not be constructed quickly enough to meet demand, and tent homes and businesses appeared throughout the settlement. The sudden population pressure drove new civic investments, including Winnett’s first sidewalks, streets, and water system. 

Production reached its peak in 1922. The Denver-based Frantz Oil Corporation had found the high-quality crude at extremely shallow depths, and its success drew oil companies from across the region to the Cat Creek field.  The field’s first producing sand zone, the largest unit and the dominant producer at the site, accounted for the majority of total output from the field’s 131 wells in that formation alone.

The corporate ownership of the field shifted repeatedly during and after the initial boom. The Elk Basin Consolidated Petroleum Company, which held controlling interest in the Frantz Corporation, sold the Cat Creek field in 1924 to the Mutual Oil Company of Casper, Wyoming, for $450,000. Mutual Oil in turn sold the field in 1938 to Continental Oil.  These successive transfers reflected both the consolidating tendencies of the petroleum industry during the interwar years and the maturing of a field that had already passed its period of greatest production.

The Formation of Petroleum County: Political Consequences of an Oil Strike

The rapid population growth and economic activity generated by the Cat Creek field had direct political consequences. The sparsely settled eastern portion of Fergus County had long felt underserved by the county seat at Lewistown, a problem that the oil boom made acute by suddenly concentrating population and economic activity in the Cat Creek basin and at Winnett. After years of failed attempts to split from Fergus County, on November 4, 1924, residents of eastern Fergus County voted to break away, and the new county government began operating on February 22, 1925. 

Sectioned off from eastern Fergus County and named for its successful oil production, Petroleum County officially became Montana’s 56th and final county in February 1925.  It remains the last county to be organized in the state’s history. The county’s name was not merely descriptive but declarative, an assertion of identity founded on a single industry. Winnett, which had grown so rapidly in the preceding years, became the county seat.

The irony embedded in this political triumph was swift in making itself felt. The growth and optimism accompanying the oil boom and the county separation lasted only briefly. Winnett went from an estimated population of 2,000 in 1923 to 408 in 1930. On the eve of the Great Depression, Petroleum County residents had already suffered the adversities of drought and depression, but none of those previous difficulties would approach the devastation of the 1930s. The severe drought that began in 1929 and reached disastrous proportions by 1931 overlapped with the global economic collapse to leave the county in desperate condition. 

Decline, Revival, and the Long Diminuendo

The trajectory of Cat Creek’s production after 1922 describes a curve familiar to extractive economies. The field that had briefly captured national attention as one of the most promising new oil discoveries in the United States settled into a long, irregular decline punctuated by occasional revivals. A smaller oil boom occurred in 1946 when oil was again discovered at Cat Creek,  and a mini oil boom in the mid-1940s caused excitement and brief speculation.  Continental Oil, which had acquired the field in 1938, maintained production through the mid-twentieth century, finding in Cat Creek a mature but still-productive asset.

By the early 1960s activity at Cat Creek had declined significantly from earlier levels. By 2012, the field was producing only approximately 24,000 barrels annually, compared to over two million barrels in 1922.  Over the entire productive life of the Cat Creek field, estimated at approximately fifty-four years, roughly 23 million barrels of oil were extracted from the field before operations ceased.  Production peaked in 1922 and continued until the last pump was shut down in the 1990s because the wells were no longer profitable. Today, interest in energy production in the area has reemerged due to promising natural gas deposits. 

The broader Montana petroleum industry that Cat Creek helped inaugurate developed significant momentum in subsequent decades. Following Cat Creek’s discovery in 1920, the Kevin-Sunburst field was discovered in 1922. Over the next forty years, additional oil fields were developed in the Williston Basin of northeast Montana, the Sweetgrass Arch of northern Montana, the Big Snowy Uplift of central Montana, and the Powder River Basin of southeastern Montana. Montana’s petroleum production peaked statewide in 1968 at 48.5 million barrels.  Cat Creek had pointed the way.

Legacy and Assessment

What remains today of the Cat Creek oil field is, in material terms, modest. The community of Cat Creek, sometimes called Frantz or Frantzville after its founder, persists as an unincorporated settlement in the eastern portion of Petroleum County. The state of Montana created Petroleum County as a direct result of the Cat Creek discovery, and Petroleum County remains the last of Montana’s 56 counties to have been formed.  Winnett, the county seat, retains the Petroleum County Courthouse, a locally quarried stone building from the town’s early years now listed in the National Register of Historic Places.

The population statistics of Petroleum County constitute, in their sparse numerical column, an implicit account of what resource extraction and its withdrawal do to communities built around a single commodity. The 1930 census listed 2,045 residents. By the 1980 census, the population had declined to 685. The 2020 census recorded 496 residents, making Petroleum County both the least populous county in Montana and among the least populous in the entire United States. 

The Cat Creek field’s historical significance rests on several distinct foundations. It was Montana’s first commercially productive oil field, demonstrating that the petroleum seepages and geological formations that observers had noted across the state for decades could, under the right circumstances, yield viable commercial production. It generated the population and economic pressure that produced a new county and brought basic civic infrastructure to a previously remote region. It attracted corporate investment from outside the state and inserted central Montana, however briefly, into national conversations about energy development. And it demonstrated, with characteristic Western clarity, how quickly a resource-dependent community can rise when the resource is abundant and fall when it is not.

The geological work begun by C. F. Bowen in 1912 and extended by subsequent researchers laid the intellectual foundation for understanding not just Cat Creek but the broader structural geology of central Montana. The Cat Creek anticline, with its complex fault history reaching back to the Proterozoic, became an important case study in the relationship between ancient structural events and the accumulation of economically significant petroleum deposits in the overlying sedimentary column. In this sense, the field contributed to regional geological knowledge well beyond its direct commercial significance.

The story of Cat Creek does not admit of easy conclusions about the value or costs of petroleum development in rural Montana. What the historical record establishes clearly is that a geologically distinctive deposit in a sparsely populated corner of the state briefly concentrated capital, labor, political energy, and public attention in a manner that left permanent institutional traces, among them a county that still exists, however thinly populated, as evidence that something consequential once happened in the Musselshell country.

Works Cited

Bowen, C. F. “Geology of the Cat Creek Oil Field, Fergus and Garfield Counties, Montana.” AAPG Bulletin, vol. 5, no. 2, 1921, pp. 252-265. GeoScienceWorld, https://pubs.geoscienceworld.org/aapg/aapgbull/article/5/2/252/546670. Accessed 15 May 2026.

Hadley, Herbert D. “Cat Creek Oil Field, Petroleum and Garfield Counties, Montana.” AAPG Bulletin, vol. 39, no. 4, 1955, p. 534. GeoScienceWorld, https://pubs.geoscienceworld.org/aapgbull/article-abstract/39/4/534/549323. Accessed 15 May 2026.

Meek, J. S. “Curley,” as told to Mike Voeller. “Cat Creek Oil Field 42 Years Old This Month.” Winnett Times, 25 Feb. 1962. Montana History Portal, Central Montana Historical Documents, Lewistown Public Library, https://www.mtmemory.org/nodes/view/3646. Accessed 15 May 2026.

Montana Legislative Environmental Policy Office. Petroleum and Petroleum Products in Montana. Helena: Montana Legislature, 2004. Montana Legislature Archives, https://archive.legmt.gov/content/publications/Environmental/2004deq_energy_report/petroleum.pdf. Accessed 15 May 2026.

Petroleum County Public Library. Pages of Time: A History of Petroleum County, Montana. Lewistown, MT: Petroleum County Public Library, 1990.

Petroleum County Historical Overview. Petroleum County Community Library, petroleumcolibrary.wixsite.com/petroleum-county/about1. Accessed 15 May 2026.

Petroleum County Montana History Portal. Cat Creek Oil Field Northeast of Winnett, Montana. Central Montana Historical Photographs, Lewistown Public Library, Montana History Portal, https://www.mtmemory.org/nodes/view/86471. Accessed 15 May 2026.

Rotness, Barbara Pepper. “Early Development of the Cat Creek Oil Fields.” Montana History Revealed, Montana Historical Society, 14 June 2016, http://mthistoryrevealed.blogspot.com/2016/06/early-development-of-cat-creek-oil.html. Accessed 15 May 2026.

Stuart, Granville. Forty Years on the Frontier. Vol. 2, Arthur H. Clark, 1925, p. 124.

Wisley, Steven T., et al. “Recurrent Faulting and Petroleum Accumulation, Cat Creek Anticline, Central Montana.” AAPG Bulletin, vol. 75, 1991. Office of Scientific and Technical Information, U.S. Department of Energy, https://www.osti.gov/biblio/6006377. Accessed 15 May 2026.​​​​​​​​​​​​​​​​