Driving east along Highway 78 through winding Sentenac Canyon, the view into Yaqui Flat signals the last bend. A slow approach through these final turns is a good idea, as the heavy guard rail on the north edge of the narrow highway warns. Old road cuts can be seen slicing abruptly across the right and left slopes of the modern highway, and just into the first straightaway is the wide Plum Canyon turnout with the road entrance to Plum Canyon at its east end.
Plum Canyon is usually best between April and May of any year, as it’s lowest elevation at the highway, around 1,700 feet, brings the wildflowers and best hiking/camping temperatures after March. Some of the coldest temperatures to be found in San Diego can be found here in midwinter. Its higher elevations (2,200′) can still mean cooler temperatures for fall visits by ten degrees, when it’s still in the 90’s in Borrego Valley.
The access to the canyon is immediate to the interpretive station at the far east end of the turnout which, incidentally, is partly carved from the old alignment of the earlier road used from Julian to Kane Springs, just west of the Salton Sea. Peter and Paul Sentenac were area cattlemen who, once upon a time, used a natural access up the west fork of the canyon for an easier pull of wagons and livestock to get to the verdant grasses at Scissors Crossing, easier at the time than the now Highway 78 which cuts through narrow and boulder-strewn Sentenac Canyon. Still, Sentenac Canyon was no picnic for highway builders when its time came around 1915, as evidenced by the derelict bridge that once spanned the narrows at about mid-canyon. The canyon is the main tributary of waters shedding off the east slopes of Julian and Volcan mountains; but farther east, as it becomes San Felipe Creek, this large volume of water runs largely underground. It can be a torrent in summer thunderstorms and in some winter storms, but is meek by the time it reaches the flat desert. One of its wells, in the area of Borrego Mountain, was a life-saver for the Anza Expedition in 1775, about 20 miles downstream from Plum Canyon.
Below: USGS inset map showing Plum Canyon access road from Highway 78 south. Take west fork (thin dashed line) going south to reach end of road (top photo below, this parking area is south end of the west fork–see dashed lines USGS map near word Plum); the trail from there resumes southerly as the California Riding and Hiking Trail. The crest of the trail, about one mile hike south, offers a very nice view of Shelter Valley (bottom photo below).
Below: Cactus blooms seem quite competitive once the decision is made by their inner clocks to produce their color. And color is the name of the game. At nearly the edge of the visible spectrum (and possibly leaving it) the plant can be seen several hundred feet away. To an insect, possibly farther. After all, the bees and beetles must be able to find these “beacons of the desert” in the limited time they have available to gather food energy.