Final answer:
The Great Plains feature characterized by large areas of tall grass is known as a prairie, which is integral to the region's agricultural productivity.
Step-by-step explanation:
The geographical feature found in the Great Plains of the US, made of large trellis areas and tall grass, is known as a prairie. These prairies are characterized by their expansive flatlands that predominantly consist of tall grasses, and the region is commonly referred to as America's breadbasket due to its use for farmland. It is one of the most fertile agricultural areas in the world, once covered by tallgrass prairies that were essential for deep, rich topsoils which have largely been converted to support agriculture such as the vast expanses of corn and wheat belts.