Anza Design & Nursery

Dehesa Beargrass (Nolina interrata) is a rare and endangered plant (California Rare Plant Rank: 1B.1) found in southern California and northern Baja. San Diego County is home to roughly 10 occurrences of Dehesa Beargrass, with a large percentage of those occurrences being on or around McGinty Mountain. [The common name ‘Dehesa Beargrass’ is actually named after the small town of Dehesa within the Dehesa Valley, which is just north of McGinty Mountain]. Like a few other rare California plants that take refuge in San Diego County, this plant straddles a geopolitical border between Mexico and the United States.

Dehesa Beargrass is a scraggly and unassumingly beautiful plant. The foliage carries a bright grey-green shine to it that pops against the muted olive tone of its chaparral habitat. On occasion, the grey-green foliage is complimented by a stalk of cream colored inflorescence (something I always seem to miss). The plant does not bloom every year and primarily reproduces asexually from an underground stem, which aids its ability to survive wildfires. In the garden, the plant has both the bold texture and the striking flower thing going on. In its habitat, the plant is perfectly accentuated by the dark tones of its stony, rocky soil, which in itself is an interesting geologic story.

McGinty Mountain itself is a rather nondescript mountain in eastern San Diego County. It lies near the towns of Jamacha and Jamul just southeast of the city of El Cajon. The mountain is somewhat of a “green island” amidst San Diego County’s sprawling east county developments. Estate residential lots wrap around the mountain’s lower slopes and while McGinty Mountain remains a semi-popular hiking spot, most east county residents largely experience it as an olive green backdrop spanning their viewshed to the east. It’s probably safe to say that most residents of San Diego County do not know that McGinty Mountain is home to the rare Dehesa Beargrass.

The geology of McGinty Mountain is composed of Cuyamaca Gabbro, which is a type of mafic rock that originated deep within a segment of oceanic crust. (That segment of oceanic crust is also know as an ophiolitic suite). Generally speaking, gabbro forms when magma from within the Earth's mantle rises to the surface along a mid-ocean ridge. As that magma rises, it oozes through layers of the Earth's crust and then slowly cools into a dense layer within the lower portions of the ophiolitic suite. The "volcanic" or magmatic origins of gabbro means it forms much like basalt and then cools more like granite, where a slow cooling process allows for the formation of large visible crystals and a dense structure. 

Gabbro soils are rich in iron, magnesium and calcium. Some plants cannot tolerate that chemistry and, as a result, gabbro soils can become a restrictive edaphic feature for other plant species growing in that area. 

Oh, and by the way, McGinty Mountain is also home to another rare plant: Tetracoccus dioicus - also a beautiful and interesting plant that seems to prefer gabbro soils. So how about that for a seemingly non-descript mountain.