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  Shan Creek Road scenic drive overlooking Grants Pass valley, southwest Oregon

Up from River Bank Road           Down from Briggs Valley Road

Shan Creek Scenic Drive

Shan Creek Scenic Drive is a ten mile route on gravel surfaced road that climbs from the Grants Pass valley to a ridge near Onion Mountain where it connects with roads that take you to Onion Mountain Lookout, Spalding Pond campground, and Briggs Valley with hiking and equestrian trails, mountain biking and campgrounds.

This route is one of the most scenic drives in the Grants Pass area but is also unique because of the dramatic influence that the geology has on the plant communities growing in this area.

Two versions

There are two versions of this guide with the mile markers arranged for travel up Shan Creek Road from River Bank Road or down from the Briggs Valley Road in the other direction. The orange block in the upper left tells you the travel direction for the guide displayed on the screen. The tan bar in the upper right provides a link that will switch you to the other direction.

Safety

The road is generally well graded but rock from road cuts may roll out into the road way, especially after rain or snow fall. Vehicles with average clearance can drive on this road but it is recommended that all vehicles have tires suitable for driving on gravel surfaces.

The upper elevations of both the Shan Creek Road and Briggs Valley Road are not passable during the winter due to snow fall.

Shan Creek Road takes into an area where you may be 10 or more miles from the nearest help. As a precaution, carry emergency supplies such as blankets, extra food and water. A day pack for carrying water would be useful if you find it necessary to walk to the nearest help.

Directions

From Grants Pass, follow Highway 199 for about seven miles to the Applegate Bridge. Immediately after crossing the bridge, turn right on River Bank Road and follow this for 5.5 miles to Shan Creek Road on the left. SET YOUR ODOMETER TO ZERO as you turn on to Shan Creek Road and follow the road guide below to find points of interest as you enjoy the drive.   
NOTE there is a store about a quarter of a mile past Shan Creek Road that sells gas and other supplies.

0.0       Intersection of Shan Creek Road and River Bank Road. The first mile of the road is paved and land on both sides of the road are private. Public land begins at about mile 1.2.

1.0       In the road cut, look on the left to see an exposure of white colored diorite with rock rubble above. Diorite was at one time molten rock associated with a series of volcanic events in this area about 140 million years ago. This type of rock decomposes into sand and is more quickly eroded away than other rocks in the region. For this reason the region that was once occupied by these ancient volcanic rocks is roughly defined by the valley around Grants Pass, which was created by the erosion of these rocks.

            It is important to understand that when these rocks formed they were about three miles beneath the surface. Over the following 140 million years, this region has been slowly uplifted at a rate of 2-3 millimeters a year. Erosion whittled the mountains down as they grew until eventually these rocks worked their way to the surface where we see them today. The mountains in this region continue to be uplifted at the same rate of 2-3 millimeters and erosion continues to wear down the mountains as they grow. The rubble of rocks above the diorite is a good example of this weathering. The ancient volcano that once sat in this region has long ago been eroded away and all we see now is the diorite, the volcanoes crystallized roots.

           The diorite seen in this road cut is located near where the molten rock of the ancient volcano meets the other rocks of the surrounding region. It is interesting that these other rocks are also volcanic but are older and formed in a very different way from those that make up the valley around Grants Pass.

1.1       Pavement ends

1.2       Shan Creek Trail
This trail is located at a small turnout on the right and takes you on a short, moderate hike to Shan Creek.

2.0       The road cuts through green-gray rocks of an ancient slab of ocean crust. Ocean crust is created by a series of volcanic events where molten material pours out of long cracks that may several miles long. This is why these are called rift volcanoes. Each volcanic event pushes the rock of older events aside causing the ocean floor to grow. The growth of ocean floors are what cause earthquakes and other volcanic events to occur such as the one that once existed in the valley around Grants Pass. This section of ocean crust was pushed up against the continent edge about 150 million years ago. High pressure and temperature changed these rocks from their original black color to the green-gray color you see now. The folding of the rocks against the continent edge also created tension that shattered and shuffled the rocks, creating a number of small fault zones. One of these faults can be seen on the left after passing through the road cut.

2.1       The ocean crust rocks of this region experienced a great deal of fracturing and shattering and this makes some parts of the mountains susceptible to land sliding. The land slide seen above the road on the left is a good example.

2.6       The road goes through another road cut that is made up of pillow basalt. These are lava flows that erupt under water and one of the characteristics of this type of eruption is the formation of rounded, pillow-sized lumps, one piled on top of the other to form what looks like a massive cluster of grapes. This is typical of the type of lava fields found where rift volcanoes erupt under the ocean.

            If you look around in the road cut on the right, you might be able to find some samples of this rock. When this lava erupted, it formed air bubbles that made the rock look like Swiss cheese. These later filled with minerals so you will want to look for samples that are freckled with small, rounded features about the size of a pin-head or BB.

            An interesting fact about the bubbles that form in pillow lava is the influence of water pressure on their size. Pillow lava that erupts in deep water is subjected to higher water pressure and this makes the bubbles smaller. In very deep water, the pressure is high enough that no bubbles will form. In shallow water eruptions, the water pressure is less and bubbles tend to be larger. The pillow lava found at this road cut is a good example of a shallow water eruption. 

2.7       After each eruption along an ocean rift volcano, sediment begins to accumulate on top of the pillow lava. At this point in the tour you are entering into some of the sediments that accumulated on the pillow lava you saw at the last stop. This segment of ocean crust was close to a continental edge so sediment, probably from nearby rivers rapidly accumulated on the ocean floor. In some exposures of rock, you might find some fossil plants that washed into the ocean from the shore.

6.1       The plant community changes dramatically at this point as the road crosses a fault line and enters a region of rocks that were uplifted from the upper mantle of the earth. These mantle rocks produce very poor soil so fewer plants tend to grow here than in the region you have been driving through on the first six miles of the tour. Shan Creek Road has one of the best examples of how the geology of this region can dramatically influence plant communities.

            Mantle rock is formally known as peridiotite but as these rocks were uplifted to where water from the surface could interact with these rocks under high pressure and temperature, most of the peridiotite was altered in varying degrees to a type of rock called serpentine. 

6.3       As you drive along this section of road, look for white-colored streaks about 2-10 inches wide in the road cut to the left. These are cracks made in the mantle rock that filled with molten rock and quickly cooled to form a black rock called diabase. During uplift of this region, water mixed with the mantle rock while it was still under high temperature and pressure changing some of the surrounding rock to serpentine. During this time, the black minerals of the diabase were drawn out leaving a white rock called roddingite. At one time these fractures probably extended for long distances, perhaps up to a mile. However, serpentine rock tends to be very brittle and during earth movement that uplifted these rocks, the cracks of roddingite were significantly shuffled. This is why you only see small segments of roddingite with no sign of the rest of the crack visible in the near vicinity. 

6.5       This vista is one of the best places to get out and look at the scenic view of Shan Creek. The exposure of mantle rock, similar to what you are standing on, forms a relatively barren area on the slope below with the contact with fertile ocean crust rocks making a distinct boundary of lush vegetation further up the slope. These highly contrasted plant communities is one of the reasons for the unique botanical diversity of this region.

           This is also a good place to experience the distinctive greasy characteristic of serpentine rock. Walk across the road to the road cut and pick up some of the fine dirt along the base of the rocks. Rub this between you thumb and fingers and you should be able to feel a slight greasy texture. This greasy feeling probably comes talc, a serpentine mineral formed along cracks as rocks rub against one another. This may be one of the reasons why these rocks tend to shuffle past one another, sliding on a "greased" surface.

7.0       The road crosses a boundary between serpentine and ocean crust. Note how the vegetation changes.

7.5       Shan Creek Overlook picnic area (right)
IIf you want to look for it, there is an informal trail across from the picnic area on the left side of the road that climbs for about about half a mile and 200 feet of elevation gain to the top of the peak overlooking the Shan Creek watershed and Grants Pass valley. This is a beautiful vista point but the hike is best suited for people who don't mind a short hike with a little bit of a "cross county" feel to it. A panorama from the top of the peak is shown below. Onion Mountain is on the far left. Grants Pass is in the distant right.
 

7.6       The road enters another outcrop of mantle rock for a short distance. Note how the dense brush growing on the mantle rock suddenly gives way to an almost barren open are above the road to the right. Enter heavily foliated serpentine. Barren meadow in saddle above road on right.

7.7       Serpentine continues but with a fairly dense forest.

7.9       Basalt begins in this vicinity. Note serpentine contrast on hill to the left.

8.2       Intersection: TURN LEFT to continue the tour. The road to the right goes to the Onion Mountain Fire Lookout, located about 2 miles from here. 

9.0       A small outcrop of black shiny serpentine in basalt on left

9.8       View toward Briggs Valley on the right.

10.1     Road 25 (Big Pine 9; Highway 199 12; Onion Mountain Look Out 4

            Pavement begins

            End Tour ZERO ODOMETER

Tour text and photography by Roger Brandt, Highway199.org

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