Motocross really took a step in the direction it is in today when Edison Dye came into the motocross picture. He ran motorcycle touring business in Europe and his travels across the pond exposed him to a new style.
Motocross came to America in the 1970’s in the form of hair scrambles. Simple off road races. The sport grew and eventually came to the LA Coliseum. Which was when supercross was invented, a form of motocross on man made courses.