Farther south in the lowlands , similar rocks are covered by the sedimentary beds deposited under the sea that once filled the midsection of the country.

• 大平原和内陆平原的边界是一趟低矮悬崖，它标志着覆盖在平原上的由落基山脉风化物沉积形成的疏松表层东部边缘。