Mt. Piyashiri-yama (ピヤシリ山, Piyashiri-yama), in northeastern Nayoro City (名寄市, Nayoro-shi) towers the great river of Northern Hokkaido, the Teshio (天塩川, Teshio-gawa). Though not as tall as Mt. Teshio-dake (天塩岳, Teshio-dake) or Mt. Uenshiri-dake (ウエンシリ岳, Uenshiri-dake), Piyashiri is certainly the furthest north of the high peaks in the Kitami Mountains, and one of the northernmost prominent mountains in all of Japan. The mountainside features a number of small marshes, while nearer the summit you’re likely to see strangely-shaped rocks and ridgelines, from which the views are beautiful.
Two hypotheses currently exist to explain the mountain’s name, both from the Ainu language: pi-shiri means ‘rocky mountain,’ while pira-shiri means ‘cliff mountain’—both could be applicable here (as elsewhere—you'll find a number of Piyashiris dotted across the island).
The trailhead sits at the far end of a forest road running along the small stream Kouzan-sawa (鉱山沢) in Shimokawa Town (下川町, Shimokawa-chou). There are no bus stops nearby so you’ll have to take your own car in, or otherwise a pricey taxi from Nayoro. At the entrance to the forest road is a gate which may be locked during the first half of the season, so it’s a good idea to check before you head out.
From the trailhead you’ll follow an old forestry trail for a little bit, then enter a quiet forest. As the trail gets steeper and you head deeper into the woods you’ll come across a small grove surrounding the Okuruma-no-taki Waterfall (御車ノ滝, Okuruma-no-taki). Around here you’ll also see a good deal of Ezo anemone.
Before long, you’ll come to Piyashiri Swamp (ピヤシリ湿原, Piyashiri-shitsugen), a marsh tucked in among the Glehn’s spruce. At the beginning of spring, you'll find plenty of white skunk cabbage and marsh-marigold clustered among the grasses. You might notice on maps that both this marsh and another on the northern flank of the mountain are both called Piyashiri-shitsugen. Make sure you've figured out which one you're in before setting off orienteering.
After rounding a series of bluffs on the upper slopes, you’ll come onto a flat ridgeline covered in Kuril sasa bamboo and dwarf stone pine. In clear weather, the summit should be visible right ahead of you. If you’re climbing in June, your eye will probably be drawn to the huge ring of white Kamchatka trillium on the lee side of the ridge as well.
From the summit of Piyashiri-dake you’ll find a surfeit of threeleaf goldthread and views over an immense part of the Teshio watershed. To the south, if you’re lucky, you should be able to catch the dim forms of the Northern Daisetsuzan (大雪山) Mountains in the distance. To the north, the low hills yield views over enormous distances.
If you continue past the summit for 200 meters or so, you’ll find a small hut that you can stay in overnight. It sits at the end of a long, winding road coming up from the nearby Piyashiri Ski Field (ピヤシリスキー場, Piyashiri sukii-jou).
During the coldest part of the Nayoro winter you can sometimes see an optical phenomenon called a ‘sun pillar.’ It’s said that the hut atop Piyashiri is one of the best places to view them. Besides this, as the temperature is generally quite low and the air is dry, the snow around here is incredible for skiing. Expect to see some backcountry snowmobilers on the northern slopes of the mountain as well.
You’ll descend by the same trail you came up.
Around mid-June you’ll see plenty of Ezo anemone all along the trail. In the marshes you’ll run into the aforementioned white skunk cabbage, as well as swamp cabbage and oriental swamp pink (a particularly strangely-shaped flower). Along the ridge you should see woolly geranium and Kamchatka trillium all summer long. The leaves on the trees start to change around the end of September.