2020 - Trip Report - Two Trees Canyon Near Riverside

Two Trees Canyon Near Riverside

by Bill Neill

I would like to share some notes on my volunteer project near Riverside, before and during the pandemic. If nothing else, DE members will learn about popular hiking trails in Box Springs Mountain Reserve, just east of the UC Riverside campus.

For those that don’t know me, I’ve been a licensed herbicide applicator for 37 years, working to control invasive non-native plants in wildland areas. For the first 17 years, while employed as a petroleum engineer, I organized volunteer work parties to remove tamarisk or saltcedar from desert springs and riparian areas. Then twenty years ago I turned professional and have worked mostly in coastal watersheds and mostly in Los Angeles County.

For the first 18 years of the past 20, since turning professional weed-killer, I traveled from L.A. County to Riverside a half-dozen times per year, to attend weed manage-ment area meetings and for invasive weed control work, either paid or volunteered. Then in January 2018, I was told by local friends about non-native castor bean plants growing abundantly in Two Trees Canyon, following a large wildfire during the previous summer.

So I obtained permission from Riverside County Parks & Open-Space District, and started spraying many thousands of young castor bean plants on the burned canyon floor, not initially appreciating the size of the volunteer project that I had undertaken.

The photo of Two Trees Canyon was taken in March 2019, after a wet winter and 20 months after the fire. The view is toward the west, with downtown Riverside at top center and the UCR campus in the upper left corner. In the lower right corner, behind a granite boulder, is a young castor bean plant with shiny palmate leaves, at one of the highest elevations in the watershed. The lower portion of Two Trees Canyon is a corridor of large sycamore trees, grey and without foliage in the photo due to winter-dormancy.

Two hiking trails extend up the canyon, from the lower trailhead near the east end of Blaine Street: one trail skirts the edge of the riparian corridor

of sycamore trees, and the other trail climbs along a ridge to the south (left side of photo) and continues to the summit, which is accessible by vehicle via Pigeon Pass Road.

For those not knowledgeable about castor bean, it is the source of a deadly poison called ricin, mentioned in newspaper articles about terrorist threats several years ago. The large beans are also the source of 

castor oil, a high-quality lubricant for race cars and still a well-known laxative. The Castrol brand of motor oil originally included castor oil added to petroleum product. More than a century ago, castor bean was grown agriculturally in Los Angeles to produce lubricant oil, before petroleum was discovered; and from there, the plant appears to have spread along railroad tracks via contaminated gravel. How and why the large seeds were transported high up Box Springs Mountain is unknown, but I suspect that seeds were released decades ago as gopher poison along now-corroded metal pipes that transported water from some of the springs.

The problem of castor bean in natural areas, especially after fire, is that the plant grows fast and the large leaves can shade out native foliage, even the resprouting sycamore trees in Two Trees Canyon. Fortunately, castor bean foliage is highly susceptible to Garlon 4 herbicide, so can be sprayed with a dilute concentration that will not harm adjacent native vegetation. Since January 2018 I have volunteered 180 hours of herbicide application in the canyon, during 29 trips to Riverside and vicinity, with expenses for herbicide and travel (but not labor) paid by a local group, Friends of Riverside’s Hills. Currently, castor bean plants are still present in the canyon but quite rare, whereas without herbicide treatment, castor bean would be abundant, if not dominant.

In my 37 years of invasive weed control work, Two Trees Canyon has been the most challenging area to access – from the combination of steep slopes, giant boulders, and abundant poison oak. But the canyon is worth visiting if you are in Riverside looking for hiking trails with a view.  ~ Bill

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