From National Route 451 (国道451号線, Doudou 451 gosen), you can see a tall, sharp peak emerging from the deep forest. This is Mt. Kogane-yama (黄金山, Kogane-yama), a low peak on the southern edge of the Mashike Mountains (増毛山地, Mashike-sanchi). The etymology of the name isn't clear, but as the word kogane means 'yellow gold', it could have something to do with the closed gold mine at the nearby Kogane-sawa River (黄金沢, Kogane-sawa).
Its shape has also given it the local nickname Hamamasu-fuji (浜益富士). Though it's not particularly high, the views are uninterrupted for miles around and the dropoffs from the summit are perilous (to say the least). Because the hike is quite short and the trip out to the mountain and back can be done comfortably within a day from Sapporo, the weekends can get quite busy.
Public transportation is somewhat lacking on this part of the island so most people take their own cars to the mountain. You'll follow National Route 451 along the Hamamasu River (浜益川, Hamamasu-gawa) away from the Sea of Japan until you see a small signboard indicating the mountain--there, you'll head into the forest on a dirt road following the Kanehira-sawa River (兼平沢, Kanehira-sawa). On a clear day you should be able to see the shape of Kogane-yama looming ahead. At the end of this forest road you'll come to the trailhead, where there is a parking lot and a small toilet.
The trail follows the Kanehira-sawa for a little ways before splitting into the New and Old Trails. Near the junction runs a little stream making for a great watering hole. The Old Trail, to the left, gets quite steep and precipitous near the summit, so head to the right up the New Trail.
You'll pass through a flat meadow before the trail starts to rise quite sharply, passing through a forest laced with tall cliffs. Here, you'll run into Anemone flaccida, skeleton flower, Viola grypoceras, and Aconitum mashikense, the last of which is distributed here in the Mashike Mountains as well as in the neighboring Kabato Mountains (樺戸山地, Kabato-sanchi). You should also be able to see Aconitum umbrosum, a cream-colored flower with fuzzy stems.
Pushing up a steep hill of Mongolian oak trees, the Old Trail will merge from the left. The ridgeline here will start to get narrower and narrower as you progress towards the summit, becoming nothing but a rocky ridgeline near the top. In late June, you'll be able to see plenty of Thunberg's fleabane, forked viburnum, and Albrecht's rhododendron around here, as well as the snowcapped peaks of Mt. Hamamasu-dake (浜益岳, Hamamasu-dake) and Mt. Gunbetsu-dake (群別岳, Gunbetsu-dake) shining in the sun.
The summit of Mt. Kogane-yama is surrounded by huge precipices and is seriously narrow. You're not particularly high up as far as Hokkaido mountains go (sub-1000 meters), but the drop-offs on either side will give you the impression that you're much higher.
The route down will follow the route that you took up.
Because the mountain isn't at a particularly high elevation, the climbing season lasts quite long (from mid-May through the end of November). Flowers start blooming in earnest at the end of May. At the beginning of summer the slopes will be packed on the weekends, so our recommendation is to try and get out on a weekday if you can. The leaves will start changing at the end of October. Seeing the first snows on the taller Mashike Mountains at the beginning of winter is also beautiful.