Joes Hill is the largest of several Hawaii type shield volcanos in the monument. It is recognizable as a low hill located 3.2 miles directly east of the I-17 sunset rest area. There have been at least six major flows of gas-free and gas-charged basalt to andesitic basalt magma from the conduit. There is very little pyroclastic material in the vent area. The top flow has been dated as Miocene (~10.8 My).
Most of the flows can be seen in the above picture. The large canyon in the right forground is the Agua Fria river, some 1,120 feet below the top edge of the canyon. The Proterozoic granodiorite starts at ~2910 feet, which is about 3/4 of the way down sunset creek canyon. The flows, which are ~583ft thick at this point, sit directly on Proterozoic granodiorite, there is only very small amounts of the slightly older Proterozoic metamorphic rocks between the two major units.
The hills in the canyon bottem are basalt slump blocks that have broken off the sides.

• View of Joes Hill from the north The Agua River has cut a deep canyon down to bedrock. The New River mountains are in the background.

• Close up view of south-west side of Joes Hill A basalt slump block can be seen to the right, in the picture. The arrow points to the vent area on top of the hill.

• Large boulder of Granodiorite with greenstone xenoliths. Picture taken at the Agua Fria river. This car size boulder has been polished by river water flow.

• Greenstone roof pendants in granodiorite. At the river, first picture

• Greenstone roof pendants in granodiorite. At the river, second picture