The postcard above and the two photographs below were all taken from a page in a photo album that bore the caption, "Girls' Band, Knoxville, Iowa, 1914-1915." A group pose (dated 1916) similar to the one above can be found in A Historical Album of Knoxville, Iowa (1991). The caption in the Historical Album states that the founder and director of the band was Larene Kurtz and that the band was active for three years during which time it gave weekly concerts in the city park.
Up until the 1920s, women and girls were frequently excluded from town bands since their presence undermined these bands' military pretensions. (The military was still exclusively male at this time.) Moreover, insofar as the town bands also served as social clubs for their members, the presence of women and children meant that the men had to mind their speech and behavior even when the band was out of the public eye, something which some of the men were loath to do. Consequently, many towns formed "Ladies' Bands" and "Girls' Bands" in order to provide the women of the community with an opportunity to play. Other towns with ladies bands included Buffalo Center, Indianola, Norwalk, and Keota.
The postcard has been physically cropped with a pair of scissors, which explains the unusual dimensions of the image. I have digitally cropped the photographs below in order to square them up, since both images were taken at an odd angle.