 Gresham Butte and Hogan Butte, in Gresham, have the steepest slopes, including a few around 50 percent.The Boring Hills, of volcanic origin, rise more than higher than the terraces to the north and west.The Kelso Slope, a northwest-sloping dissected surface west of the canyon of the Sandy River, tilts down from about above sea level near Sandy to about above sea level east of Gresham.