The term Jasper is used here as a catch-all word for different varieties of cryptocrystalline quartz, such as chert, flint, chalcedony and agate. These forms of very fine-grained quartz are very common and occur in a number of different geologic environments. The more complexly patterned and colorful varieties are often associated with, and found within, silicic volcanic rocks. The jasper is formed as a chemical precipitate in fractures and voids in the host volcanics from silicon rich fluids moving through the rock. Changes in colors and patterns are related to variations in fluid flow and minor element variations, such as a change in the amount of iron or magnesium in the precipitating fluid.

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Gary Green Jasper, also known as Larsonite, is found in Malheur County, Oregon near the town of McDermitt on the border with Nevada. It is associated with the volcanic deposits of the Pacific Northwest. It is different from many jaspers in that it has been interpreted to be a silicified bog deposit. The bog formed in the vicinity of the volcanic activity and was later covered by volcanic rocks that supplied silica to the ground water system. The silica was redeposited from the ground water into the bog sediments, replacing and preserving the original material with jasper.

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