How many letters does the top answer for “a long depression in the surface of the land that usually contains a river” have?

The most common answer is vale (4 letters).

Crossword clue: a long depression in the surface of the land that usually contains a river

2 answers found in Letterora's clue database (Wikidata facts, Open Trivia DB, WordNet and Webster definitions — all licensed sources).

vale 4 letters wn-def

a long depression in the surface of the land that usually contains a river

valley 6 letters wn-def

a long depression in the surface of the land that usually contains a river