valley floor, bottom of a gorge, bottom of a ravine
谷間【たにま】
valley, ravine, gorge, chasm, cleavage (of breasts), part or place that has been left behind, blind spot, bottom (of society), (economic) trough, gap (in activity, one's work, etc.), lull, opening
渓谷【けいこく】
valley (with a river running through it), gorge, ravine, canyon