Not far from Mashiko is area that contains a temple, 2 shrines and a cemetery – All related to the Utsunomiya clan.. There’s a lot of history in this one small area.
Jizoin Temple (1338-1574)
Okura Jinja (807)
Tsuna Jinja (1194),
Cemetery of the Utsunomiya Clan (1194). The cemetery has 33 generations of Lords of the House Utsunomiya
This is the only reference I can find with any detail at all from the Samuri Archives:
The origins of the Utsunomiya of Shimotsuke are somewhat vague but the first to adopt that name was Utsunomiya Munetsuna. The Utsunomiya supported the Southern Court in the early Muromachi Period but eventually submitted to the Ashikaga. In the 1380’s they became involved in a dispute with the Ôyama family that escalated into the Ôyama no Ran. They were weakened in the Sengoku Period by outside perils and came to rely first on the Yûki and later the Satake. They lost their lands to Hideyoshi in 1597 and with the death of Kunitsuna in 1607 drifted into obscurity.
And one Japanese link House Utsunomiya