ABSTRACTSprings with observed yields totalling about 10,000 gal/min discharge along both sides of the Colorado River in Marble Canyon, Arizona, between river miles 30 and 34.5. The waters originate from the plateaus on the respective sides of the canyon and are conducted to the floor of the canyon along the Fence fault zone or associated fractures. Chemical quality and temperature data demonstrate that some of the water discharging from springs on the west bank actually originates east of the river. This water flows under the Colorado River in the Fence fault zone, where it mixes with water from the west side before discharging from springs along the west bank. This is an unusual occurrence for the area and results because the heads at the springs along the west bank are the lowest in the circulation system associated with the fault.