This is the 4554th most frequent Japanese word.
平川
"平川" (Hirakawa) typically refers to a flat river or plain river, and it is also used as a Japanese surname or place name.
Here, '平川' means a flat expanse or plain, describing a geographical feature.
見渡す限り平川が続いている。
As far as the eye can see, a flat plain continues.
In this usage, '平川' refers to a peaceful flowing river, often used in a poetic sense to evoke tranquility.
その詩では穏やかな平川が描かれています。
That poem describes a calm stream.
In this case, '平川' is used as a family name.