The Chukchi Plateau can be described as a fragment of the continental margin jutted into the abyssal part of the Arctic Ocean. The Chukchi Plateau has the most direct connection with the adjacent shelf of the East Siberian - Chukchi continental margin. The principal structural complexes of the consolidated continental crust continue uninterrupted between the Mendeleev Ridge and Chukchi Plateau with total thickness of 26-29 km and approximately equal thickness of the upper and lower crusts under the Chukchi Plateau. In the Chukchi Basin the Earth's crust is 20 km thick with upper crust - 3 km. The Chukchi Basin, with its undisturbed sedimentary complexes, also includes 1200 m of pre- Upper Jurassic (Upper Ellesmerian) formations. Almost complete absence of folding and faults in the Chukchi Basin may point to active sedimentation, not the attenuation of the crust, as a principle cause of its subsidence. Miocene-Pleistocene complex above the pre-Miocene unconformity continues from the Chukchi Basin to the Chukchi Plateau and marks the end of formation of these present-day morphological structures.