Welcome to Rocky Star Geology

Rocky Star presents:

GEOLOGY OF THE SUSAN RIVER CANYON
and Its
FEATURES ALONG THE BIZZ JOHNSON TRAIL

The Susan River Canyon is located directly west of Susanville, California. The Bizz Johnson Trail, which follows the Susan River, offers interesting contrasts in scenery and geology. These differences exist because the Susan River Canyon is located at the intersection of four major geologic provinces. The northern tip of the granitic Sierra Nevada Range, the southern tip of the Volcanic Cascade Range, the southeastern tip of the basaltic plains of the Modoc plateau and the far west edge of the ancient sedimentary beds of the Great Basin. The characteristic difference of each of these provinces along with geologic forces such as erosion, weathering, faulting, river down-cutting and river meandering have contributed to the visible geologic features that exist in the canyon today.
The Bizz Johnson Trail head, on Lassen Street, can be looked at as the far west border of the Great Basin. Looking back in an easterly direction you'll see a gradual slope leading to the flat sedimentary beds of the Great Basin. This particular area is known as the Honey Lake Valley. While traveling through the Honey Lake Valley, wave cut terraces, created by ancient lakes that were a direct result of melting glaciers after the ice age, are evident. Susanville is located in this terrace area. Gravel alluvium, sand dunes, and Quaternary lake deposits are characteristic of the Honey Lake Valley.
Venturing east along the Bizz Johnson Trail geologic features quickly change and are dominate by volcanic land forms. Thermal activity deep below the surface is clearly represented by the numerous hydrothermal vents (hot springs) in the area. This is due to faulting in the area allowing ground water to seep deep into cracks, created by the faults, until it come into contact with molten material. The steam created by this contact creates pressure that forces hot water to the earth's surface. Historically, Susanville has tapped into these springs to provide power and hot water for the community. Today many wells are closed however, a few are still used, mainly for use in schools, public buildings, and a few homes.
As you move further west up the trail, Pleistocene and Tertiary lava flows become the main focal point. These lava flows are a direct result of the volcanic activity of the Cascade range. The Pleistocene lava flow is approximately 1 million years old and the Tertiary flow is much older, at approximately 10-11 million years old. Over time the erosional force of the Susan River has cut through these flows to uncover the beautiful basalt and andesite formations that are characteristic of these types of flows.
Beyond Cady Spring, there are many more interesting basalt and andesite formations. Further west on the trail between Devil's Corral and Goumaz, granite is exposed in railroad grade cuts and at isolated outcrops. The granite is part of the 'northern most reaches of the Sierra Nevada range. Volcanic beds from the far southwestern edge of the Modoc Plateau become more prominent in this area also. These land forms however, are much older than the surrounding volcanic flows and are thus buried and sometimes hard to find.
The following pages offer more data attempting to enhance the understanding of some of the complex terminology used in geology. A map is also provided to point out excellent examples of the interesting geologic features in the Susan River Canyon along the Bizz Johnson Trail.
Fig .1  The Susan River meandering through the Susan River Canyon. Note the gravel bars.
Fig. 2.   A broad overview of the geologic provinces in Northern California. Note the 4 geologic provinces converging near Susanville.
Geologic strata in the Susan River Canyon are not yet fully researched. Because of this hypothetical data is necessary to describe the underlying rock formations. The two figures that follow suggest possible underlying strata formations in two distinct areas in the canyon.

Fig. 3.   Position of lava flows in relation to one another in the area of the second bridge on the trail near mile 1. Notice how the Susan River has removed material between these two differently aged flows through its natural erosive process of down cutting.

Fig. 4.   Position of the lava flows in relation to one another in the area of Cady Spring. Notice the erosional effects through the weaker clastic material in the Pleistocene lava flow. Clastic material (frothy lava flows) erode faster than Basal or Andesite because, during rapid cooling, their minerals are less organized and are thus weaker internally. The erosional effect left a remnant of the Pleistocene Basal on the other side of the river.

Susan River Canyon Geologic Features ¹

1.	Along the trail between the Lassen Street Trail head and Hobo Camp, for approximately ½ mile, dark Pleistocene volcanic basalt rocks can be seen on both sides of the trail. Notice small formations of columnar basalt and its vesicular texture. The volcanic flow that settled to form these rocks is approximately 1 million years old.
2.	200 yards past the Miller Road crossing on your left, heading west on the Bizz Johnson Trail, you will see a green shed-like structure. This is known as a Stilling well. It is used in conjunction with the gondola approximately 100 yards further up the trail to measure the height of water and the amount of flow in the river. These measurements are used to calculate erosional effects on the river basin and measure seasonal runoff.
3.	The trail you are walking on is made up of various railroad ballast materials imported from other areas. These materials consist of tuff, cinder, cemented calcium deposits, basalt and andesite. The whitish cemented calcium rocks (also known as Caliche) were imported from the east side of the Honey Lake Valley where they were formed underwater when ancient Pleistocene lakes covered the area.
Fig. 5.   Imported ballast materials being dumped between railroad ties for support of the rails above.
4.	Heading west on the left side of the trail, approximately 25 yards before the first bridge is an excellent example of a cemented calcium deposit. It is white in color and has a rough surface. Cemented calcium deposits are created by the mineral reactions in hydrothermal vents (hot springs), when the material they extrude comes in contact with cooler lake water and is dispersed and deposited in the surrounding lake bottom.
5.	High above the trail on the north side is a formation of columnar basalt formed by a lava flow during the Pleistocene era. To the residents in the area this formation is known as "Pigeon Cliffs".
6.	Number six represents the area of Hobo Camp. Deposition of sediment material from granite decomposing far upstream as well as sediment materials from the overwhelming amount of volcanic rock can be seen in the various sand and gravel bars throughout the area. River meandering in this location is evident from the widening of the river basin as well as the numerous small meander scars located in areas away from the river's course.
7.	Standing on the second bridge facing south, the first visible evidence of a late(?) Tertiary lava flow is clearly seen. Notice the dark brown dirt that is characteristic in this area. This is due to the slower cooling of the molten material creating a more olivine based basalt. When weathered, the minerals making up the surrounding soils are darker. This formation continues up the canyon for many miles.
8.	After the 1 mile marker, located on the north side of the trail just beyond the second bridge, you will notice many talus slopes (rock falls). These slopes are created by the weathering of Pleistocene basalt located in visible cap formations far above the canyon.
9.	Watercress Spring runoff flows directly under the trail in a moist riparian rich area. Watercress Spring is caused by groundwater following a fault sheer zone which allows water to eventually come to the surface.
10.	Approximately 150 yards past Watercress Spring, on the north side of the trail, keep your eyes open for severely discolored, oxidized basalt. This small area shows evidence that a hydrothermal vent (hot spring) was once active and is now sealed off by accumulation of materials. The discoloration of the basalt was created by alterations of the minerals in the rock caused by the reactant minerals in the hot spring.
11.	Just beyond the two mile marker you will venture through a narrow pass of andesitic basalt. Notice the lighter color and the glassy minerals in the texture of the rock. See rock origin chart in terms and definitions section for more information.
12.	Standing on bridge number three facing north, focus on the round boulders in the stream bed. Then look directly above the river at the angular boulders on the slope of the canyon. This area is an excellent example of the erosional effects on the rocks that enter the river. The running water of the river moves rocks downstream. Over time they become rounded and smaller in size, eventually eroding the softer minerals in the rock and leaving the hardest mineral quality (sand) which is formed on the beaches along the river.
13.	A southern view from bridge four offers an up close view of the late(?) Tertiary basalt formation mentioned earlier. Notice the dark lichen on the rock. This forms due to the shading characteristic of the north facing slope it is on which provides a cooler moister climate that is favorable for this type of lichen.
Fig. 6.   Southern view from the bridge observing late(?)Tertiay Basalt flow.
14.	Just past the fourth bridge facing north, you will see up close, evidence of the bottom of the Pleistocene lava flow. Notice the rounded rocks and the clay type sediment beneath the small columnar basalt formation. This area is probably the far southern tip of the upper edge of this 1 million year old Pleistocene lava flow.
15.	Where Cady Spring runoff passes beneath the trail looking to the north on the right side of the run off, you will see a small basalt crag. This small crag most likely formed due to erosional effects of the river long ago.
Fig. 7.   Pleistocene Basalt crag near Cady Spring.
16.	Like Watercress Spring, Cady Spring is caused by groundwater following a fault sheer zone which allows water to eventually come to the surface. You will notice that Cady Spring has a greater flow of water than Watercress Spring. Susanville has tapped into this source to fulfill the needs of water in the community. A pipeline traverses the upper slopes of the canyon's north wall for two miles. Water in the pipeline flows from this natural spring to large holding tanks located just west of Susanville along Highway 36.
17.	As discussed in the introduction, the Bizz Johnson Trail offers many more interesting geologic features further west along the trail. There are more beautiful columnar basalt formations and features such as, granite outcrops, cinder (ash) beds, capstone pinnacles and much more.
Fig. 8.   One of the tunnels above Cady Spring on the Bizz Johnson Trail drilled through late(?) Tertiary Basalt and various layers of clay sediment.

Geologic Terms and Definitions

Geologic Time Scale