Most of the gas discovered in this region is found in rocks of Miocene, Pliocene, and Pleistocene age of terrestrial or lake-bed origin. Most of these rocks are associated with igneous intrusions and lava flows of Miocene, Pliocene, and Pleistocene age. The gases produced from this region not only have high methane and ethane content but an unusually high nitrogen content. They exhibit several characteristics which are more similar to the gas produced by destructive distillation of oil shale than to normal natural gas associated with petroleum. Strong evidence suggests that these gases were derived from algal and sapropelic deposits in lake beds. They are usually accompanied by a strong odor of hydrogen sulphide and large quantities of free ammonia in highly heated waters.
Gases, occurring in isolated areas of marine rocks of Cretaceous and Tertiary age, are limited in extent and possess characteristics and associations more normal and similar to other natural gas occurrences in the United States. None of the areas described has attained considerable commercial importance.