Groups that emerged from the American psychedelic scene about the same time included Iron Butterfly, MC5, Blue Cheer and Vanilla Fudge. San Francisco band Blue Cheer released a crude and distorted cover of Eddie Cochran's classic "Summertime Blues", from their 1968 debut album Vincebus Eruptum, that outlined much of the later hard rock and <answer>heavy metal</answer> sound. The same month, Steppenwolf released its self-titled debut album, including "Born to Be Wild", which contained the first lyrical reference to <answer>heavy metal</answer> and helped popularise the style when it was used in the film Easy Rider (1969). Iron Butterfly's In-A-Gadda-Da-Vida (1968), with its 17-minute-long title track, using organs and with a lengthy drum solo, also prefigured later elements of the sound.
The lyrics to "Born To Be Wild" contain the first reference to what hard rock style?
heavy metal