Morokubo-sawa (モロクボ沢) - Sawanobori in the Tanzawa range

Route Name:  Morokubo-sawa (モロクボ沢)

Trailhead:  Nishi-Tanzawa Visitors Centre (西丹沢ビジターセンター)

Map sheet:  28 [Yama-to-kougen-chizu (山と高原地図) series]

Time:  6 hours round trip / 3 hours for the sawa climb

Grade:  Overall grade 1 route

During the summer months, when Tokyo and its residents are melting in the stifling heat and humidity, there’s nothing better than getting out into the mountains and cooling off in a mountain river. The Japanese activity of sawanobori, or river climbing, involves starting at a convenient point at the entrance to a valley and tracing the course of the river upstream, walking and scrambling up the riverbed and climbing or bypassing any waterfalls along the way, until you reach the absolute source of the stream.

With a full range of grades and guidebooks, there is plenty of scope for getting into trouble in this esoteric activity, and escape would almost always be difficult in the event of a serious injury, so it is a good idea to start with something easy and less technical or committing.

One such introductory outing is Morokubo-sawa in the western end of the Tanzawa range on the outskirts of Tokyo. With straight-forward technical difficulties and an easy approach and descent, this offers all the ambiance of sawa climbing with little of the risk associated with the more technical routes.

Getting there:

If travelling by public transport from Tokyo (東京), take the Odakyu train line from Shinjuku (新宿) to Shinmatsuda (新松田) station on the edge of the Tanzawa (丹沢) range, and then take a bus (¥1180, about an hour) from outside the station to the Nishi-Tanzawa Visitors Centre (西丹沢ビジターセンター). This is the start of the walk-in.

Approach:

From the bus stop walk up the road past all the campsites along the river on your left. Keep following the road and after about half an hour you will come to a small bridge on your left. 

Cross this bridge and follow the hiking trail into the bottom of the Morokubo-sawa valley. Continue along this hiking trail with the river on your right until you come to the entry point, marked with red tape on a tree by the river, with a small artificial dam up ahead. This is the start of the sawa climb.

Entry point:

Topographical route map:

Description:

Cross the sawa and follow the right side past the man-made dam and keep walking upstream. You will soon come to the 30m Ōtaki (大滝) waterfall, the largest fall in this sawa. 

To bypass it scramble up the steep muddy slope on the left to gain an arête which takes you up a short way to a thin trail that contours along the slope above the waterfall. At the end of this traverse you will come to a short down-climb with a fixed rope. From the bottom of this just traverse a bit further round and you will get back to the sawa.

Now that you are past the Otaki the relaxed fun begins. For the next two or three hours just hike along the river bed upstream, climbing any short steps and waterfalls that you meet. There is nothing more that requires a rope and protection, so enjoy the journey.

Pay attention to the topo map and be careful when you reach any forks in the sawa. The first major fork is Honshina-sawa (本品沢) coming in from the right. The ratio of flow at this point is 3:1, with the main Morokubo-sawa providing 3x the water volume that is coming in from Honshina-sawa, so make sure you stick to the main sawa here.

About 20 minutes further on there is another fork with a 1:3 ratio, so take the right-hand fork here. The final fork comes after you have passed the last set of small waterfalls and features a 3:2 ratio. At this point you need to take the left branch.

Some way up you will reach the point where the water flow ends at the top of the sawa. Fill up your drinking water here if you’ve run out. Continue up the valley through jumbled moss-covered rocks and trees until the slope begins to steepen. There are various options around here, but try to follow the way that looks easiest, whilst always bearing to the left towards the main ridge.

Eventually you will need to climb up some rather steep mud slopes to gain the final arête that will take you up to the main ridge and the hiking trail. You should pop out onto the trail a short way below the 1293m summit of Mt Azegamaru (畦ヶ丸) on hiker’s right.

To get back down to the Visitors Centre bus stop just follow the hiking trail down the ridge. It takes about 2 hours to descend, and the last hour or so follows the Nishizawa (西沢) riverbed.

Overall:

A fun and gentle hike up a beautiful sawa with minimal technical difficulties, ending almost directly at the major western summit of the Tanzawa range. No rope or rack is needed, although a 30m rope and a belay would provide additional security to anyone with less confidence on the down-climb near the Ōtaki.