Château de Yokotashiro, Castle ruins in Tōno, Iwate Prefecture, Japan

Yokotashiro Castle, also called Gomadō Castle, is a hilltop fort site in Tōno, Iwate, on the Gomadō hill above the Sarugaishi River. Its plateau measures about 300 by 200 metres and retains broad dry moats; samurai residences and a market stood below. No stone walls are recorded.

Tradition credits Asonuma Chikatsuna, second son of Asonuma Hirona, with founding the castle on Gomadō-yama in 1189 or during the Jōkyū era (1213–1219); the construction date is unknown. The Asonuma clan ruled from here for centuries, but repeated floods of the Sarugaishi River led them to build a new castle on Nabekura-yama, and the site was abandoned by the Tenshō era (1573–1593).

The castle belonged to the Asonuma clan, who moved their seat to Nabekura-yama when floods of the Sarugaishi River repeatedly cut off retainers living on the opposite bank. The site kept the name Yokota after the move, and the old residence gave the later Nabekura Castle its alternative name. Below the castle stood retainer residences and a market known as Ichinichi.

The site lies in Tōno, Iwate, on the Goma-dōyama plateau above the Sarugaishi River, a slope of about 300 by 200 metres bordered by ravines on both sides. Look for the wide dry moats cut across the plateau. The castle town below held retainer residences and a market known as Ichihichi.

The castle is also called Gomadō Castle, after Mount Gomadō where it stood. Its plateau, about 300 by 200 metres, still shows wide dry moats, and the site is certified as a Tōno Heritage property by the city.