The Ozarks are an old mountain range, pushed up from an old seabed, then weathered back to the hills we know today. Trout had their origins in the seas existing during the Paleozoic period more than 100,000,000 years ago, when chromosome numbers and DNA content of an ancestral fish doubled, separating the evolutionary line Salmoniforms that ultimately led to trout and salmon, from the line that led to the smelts. From that distant origin, three major branches evolved, leading to the present white fishes, grayling, and the trout, salmon and char group. This separation occurred during relatively recent times, during the Tertiary period only 30 or 40 million years ago. Trout and char are separated by the presence or absence of teeth on the volmar bone in the roof of the month.
Trout have teeth along the length of the bone and char only on the front end of the bone.
The Ozark uplands were elevated above sea level by a series of uplifts during the late Paleozoic and have remained above sea level since that time. This happened about the same time as salmonids were first evolving in the sea, effectively blocking access to the sea during the time when speciation was happening. There have been several major uplifts, the last happening in the Tertiary period. The ice age, which produced four major glacial periods, reached only into north Missouri, down to the Missouri River, leaving the Ozarks largely untouched. But they influenced the climate and distribution of some northern fish species.