McMahon, a Lake Forest native, is the son of renowned local artist Franklin McMahon. He writes, "my on-location style of drawing and painting comes from my father ... who influenced me as a child not only in style but in his search into art processes."McMahon studied drawing under Al Pounian at Barat College and apprenticed at American Graphics in Chicago. He majored in art and psychology at Adams State College in Colorado and studied art history at Loyola University. The McMahon Art Gallery, featuring the work of several family members, is at 321 S. Ridge Road, Lake Forest
The Centennial art created by McMahon depicts the Library entrance, populated with passers-by. The artist notes that the drawing was done on location and painted in his home studio.