Final answer:
A lithologically-distinctive unit with recognizable contacts and traceability across exposures is known as a formation, a fundamental rock unit named after where it was first studied.
Step-by-step explanation:
The fundamental unit in geology that is lithologically-distinctive, has recognizable contacts with other units above and below, and can be traced across the countryside from exposure to exposure is called a formation. A formation is considered a fundamental rock unit that is based on similar characteristics in lithology, such as color, mineralogy, and grain size. Formations may represent deposition over various time intervals, may be composed of materials from several sources, and may include breaks in deposition. These formations are typically named after the geographic features where they were initially studied. It is through studying formations and the stratigraphic column that geologists can interpret Earth's history and the processes that have shaped it.