Country music is usually used to refer to honky tonk today. Emerging in the 1930s in the United States, honky tonk country was strongly influenced by the blues, as well as jug bands (which cannot be properly called honky tonk). In the 1950s, country achieved great mainstream success by adding elements of rock and roll; this was called rockabilly. In addition,from Swing and bluegrass emerged as a largely underground phenomenon. Later in the decade, the Nashville sound, a highly polished form of country music, became very popular. In reaction to this, harder-edged, gritty musicians sprung up in Bakersfield, California, inventing the Bakersfield sound. Merle Haggard and similar artists brought the Bakersfield sound to mainstream audiences in the 1960s, while Nashville started churning out countrypolitan. During the 1970s, the most popular genre was outlaw country, a heavily rock-influenced style. The late 1980s saw the Urban Cowboys bring about an influx of pop-oriented stars during the 1990s. Modern bluegrass music has remained mostly traditional, though progressive bluegrass and close harmony groups do exist, and the sound is the primary basis for jam bands like the Grateful Dead .