This location gives the crater a notably oval appearance due to foreshortening, although the formation is actually relatively round.

The ancient rim of Arnold has been worn and rounded by ages of subsequent bombardment.

The northern half of the rim is the most intact, particularly to the northeast where is joins the satellite crater Arnold A.

The inner floor of Arnold crater has been resurfaced by lava, and is relatively flat except for a number of tiny craterlets.

By convention these features are identified on lunar maps by placing the letter on the side of the crater midpoint that is closest to Arnold.