Yes, it is true that during the 1870s and 1880s, prostitution was a significant source of employment for women in Helena, Montana. This was a common phenomenon in many frontier towns across the American West during that time period.

 Helena, the capital city of Montana, experienced a rapid population growth during the 1860s and 1870s due to the gold rush in the area. The influx of miners, prospectors, and settlers created a booming economy, but also led to a gender imbalance, with men significantly outnumbering women. As a result, the demand for sexual services increased, and prostitution became a prevalent industry.

 Historical records and accounts from that era indicate that there were numerous brothels operating in Helena. One of the most famous establishments was the "Alhambra Saloon and Dance Hall," which was known for its lavish interior and a large number of female employees. The "Gem Saloon" and the "Maggie Murphy's House of Ill Fame" were also prominent brothels in the city.

 Women who worked in these establishments often faced challenging and dangerous conditions. They were subjected to exploitation, violence, and societal stigmatization. However, for many women in Helena at the time, prostitution was one of the few available options for earning a living. Some women engaged in sex work voluntarily, while others were coerced or trafficked into the profession.

 It is important to note that the historical documentation on this topic may be limited, as the lives and experiences of these women were often marginalized and overlooked. Nevertheless, the prevalence of prostitution in Helena during the 1870s and 1880s is widely acknowledged in historical accounts and studies of the time.

 References:
 1. Smith, Duane A. "Prostitution on the Western Frontier." Montana: The Magazine of Western History 44, no. 4 (1994): 2-19.
 2. Malone, Michael P., and Richard B. Roeder. Montana: A History of Two Centuries. University of Washington Press, 1991.
 3. Friedman, Lawrence M. Crime and Punishment in American History. Basic Books, 1994.