People often ask about the old bathhouse stone walls that now contain the Feather River Nature Center down by Old Ferry Road. The structural walls, built in 1935, were sturdily constructed of greenstone, with white "spider-web" grouting set in the seams.
The railroad runs on the slope above the center, and when the tracks were laid in 1907, they had to smash through a belt of greenstone, and the bathhouse builders used that rock in crafting a marvelous structure that proved quite durable.
Outcrops of greenstone appear all along the river road leading to the upstream Diversion Pool dam. Greenstone is not to be confused with greenish serpentine that is found in the Feather River Canyon, or with green jade also found in the river. Interestingly, the geology changes on the other side of the river where the basalt of Table Mountain and black shale behind Longbar Monument dominates.
One fine December day, I made my way to the new trail that the Department of Water Resources built from the dam along the pool for half a mile to a new pedestrian/equestrian underpass at the railroad crossing.
The bulldozer had to plow through red clay and some formidable greenstone boulders to complete the classy connection with the upper trails. Now it is graveled and ready for river watchers to use and see some wildlife and towering pines ... and some greenstone!
The Diversion Pool is a nice, steady, body of water, unlike Lake Oroville that fluctuates wildly. The pool would seem to be attractive to waterfowl but it is deep without shallow feeding areas that make the valley marshes, such as Gray Lodge, so attractive to vast numbers of snow geese and ducks during the winter. The diving mergansers are more prone to use the Diversion Pool, although other waterfowl will rest on the surface.
Left behind from the trail work are shattered boulders of greenstone. The dull greenish color is quite evident in a broken piece because some green minerals — epiode, actinolite, chlorite — are involved in the composition of the very ancient rock.
Greenstone is a metamorphosed volcanic magma, reformed by heat and pressure deep in the Earth's crust. Some greenstone developed at the bottom of the ocean during the Archean Age, about 2 billion years ago.
Table Mountain is volcanic basalt about 20 million years old, but local greenstone made its changes about 80 million years ago when the Oroville area was beneath the sea long before the Sierra Nevada granite batholith appeared (six miles deep, 90 miles wide, and 140 miles long.)
New road cuts and excavations always attract my rockhound curiosity, and I was watching for any uncovered keepers. The tall hill to the right of the trail could handily be named "Greenstone Hill" because that is the major rock in the jumbled heap, much of it excavated when the tracks were placed.
Then I noticed a yellowish "stone" that was unlike the rest. Knowing that gold is sometimes connected to greenstone formations, and a 54-pound nugget was found a dozen miles upriver, I thought I had found my bonanza at last!
I pulled it loose and it was heavy, and eagerly I brushed the soil away. But fooled again! It was a 20-pound chunk of rusty iron!
Across the pool from the trail you can see the small forest covering the Thompson Flat Cemetery, and in the same area a diamond mine was once dug. Gold dredgers had burrowed into the stream beds running down from Table Mountain, leaving behind mounds of cobble stones.
History abounds in that trail region, and once in gold days when the pool was a river, the channel was diverted by the great Chinese wall to expose the riverbed for mining.
You can continue on beyond the new trail, following the Diversion Pool along the old railway road and continue on, through the tunnel, past Longbar pond, and reach Oroville Dam.
All of those wonders await you in a land of historical richness even as it has been a land of recovery from Gold Rush and dam-building devastation. Besides the regenerated timberland and wildlife recovery to see, there are signs of previous Native American tribal occupancy and remnants of the golden past, all spread out beyond the Bath House Nature Center ... for those who, in the love of nature, hold communion with her visible forms.
"The whole wilderness seems to be alive and familiar, full of humanity. The very stones seem talkative, sympathetic, brotherly."
— John Muir