It’s been about a month and a half since Tropical Storm Hilary soaked Southern California with record-setting rainfall.
The unusual amount of Summer rain has resulted in a second Spring at Ahmanson Ranch, with some plants behaving as if it were March or April.
Not only are plants growing as if it were Spring, some are flowering. The lupine pictured above usually blooms at Ahmanson Ranch in March, April, and May. Now, as a result of T.S. Hilary’s rain, it’s flowering in October!
Those plants that usually flower in the Fall, such as telegraph weed, vinegar weed, and common sunflower, are much more widespread than usual.
Spring-like conditions are present in many areas of Southern California. On Sunday, I ran the Phantom Trail in Malibu Creek State Park. Some sections were so overgrown that it was challenging just to navigate the trail, much less run it. Ticks were also a problem.
Tropical storms are a different kind of weather beast than usually seen in Southern California. The warmer air associated with such storms can carry much more water and produce unusually high amounts of precipitation.
The rain resulting from Tropical Storm Hilary shattered many daily and monthly records. Over decades of record keeping, most stations in the greater Los Angeles area had previously measured only a trace of rain on August 20 or 21, or at best, a few hundredths of an inch. Some stations had never recorded any rain on these days.
The highest rainfall amounts occurred where the precipitation was enhanced by mountainous terrain. The northeast-facing slopes of the eastern San Gabriel Mountains, near Wrightwood, were ideally positioned in Hilary’s circulation to enhance rainfall. The Big Pine RAWS recorded over 6 inches of rain for the storm, Lewis Ranch slightly over 7 inches, and Lytle Creek nearly 10 inches.
Curious to see some of the local impacts of the storm, I ran at Ahmanson Ranch on August 22 and then a few days later at Malibu Creek State Park.
My West Hills weather station, about three miles from Ahmanson Ranch’s Victory Trailhead, recorded 3.86 inches of rain for the storm. After an initial technical hiccup, the Cheeseboro RAWS, overlooking Las Virgenes Canyon, recorded 3.52 inches of rain. This and other data suggest rainfall amounts in the Ahmanson area of at least 3.5 – 4.5 inches.
My Ahmanson run started at the Victory trailhead, went out East Las Virgenes Canyon, through part of Las Virgenes Canyon, and then up to Lasky Mesa. With that much rain, I was sure I would be wallowing in the mud and wading the creek crossings. But my shoes didn’t even get muddy!
As Hilary moved northward in California, the counterclockwise circulation of the storm increased the rainfall in the Santa Monica Mountains. Automated RAWS stations in Topanga, the Malibu Hills, and in Malibu Canyon recorded 4.0 to 4.5 inches of rain during the storm. CNRFC gridded precipitation data indicated higher amounts in some parts of the range.
On August 27, I ran the Bulldog Loop in Malibu Creek State Park. The run started at a small parking area at the junction of Malibu Canyon & Piuma Roads. As I was running up the Tapia Spur Trail, I wondered if State Parks had — as a precaution — removed the seasonal bridge across Malibu Creek on the Crags Road Trail. On August 19, the day before Hilary drenched the area, the bridge had been in place for the Bulldog Ultra. If it wasn’t removed, did Malibu Creek get high enough to damage it?
It looked like Malibu Creek State Park received more rain than Ahmanson Ranch. There was slightly more erosion on the dirt roads and some small sluffs/slides, including one tree that slid onto Mesa Peak Mtwy fire road. A tree had also fallen near the beginning of the Forest Trail.
Back at Ahmanson on August 31, things were drying out, but it was beginning to look like Spring. Grass was sprouting all over Ahmanson Ranch. It will be interesting to see if the grass survives the inevitable heat and grows enough to turn the hills green. The little bit of rain and cooler weather over Labor Day weekend will help. Some out-of-season wildflowers could also result from a false Spring.
Yesterday, I did a run in Topanga State Park, and the story was much the same. There was some minor erosion on the fire roads, but none of the larger sluffs and slides seen during the rainy season. There was no new damage to the Musch or Garapito Trails. It did look like the flow had increased on Garapito Creek with Hilary’s rain, and there was a still little water in the mainstem of the creek.
It was a little past 3:00 in the afternoon when I passed this straight-backed wooden chair along an Ahmanson Ranch trail. The Tempe thermometer clipped to my pack read over 100 degrees.
It gets REALLY hot at Ahmanson Ranch (Upper Las Virgenes Canyon Open Space Preserve). In the direct sun the temperature can be 10°F-15°F hotter than in the shade, and there is very little shade at Ahmanson. In-the-sun temperatures of 100°F or more are common in the Summer but can occur just about any time of the year.
There are two weather stations I use to get an idea of the weather conditions at Ahmanson Ranch — the Cheeseboro RAWS and Valley Circle Estates Weather Underground station. Weather station thermometers are usually shielded from the direct sun by a white, ventilated enclosure. The Cheeseboro RAWS includes a measurement of the “Fuel Temperature.” This is generally a better indication of the temperature experienced by a runner, hiker, or rider in the direct sun.
Update on July 29, 2023. Rounding the temperature to whole degrees, my West Hills weather station recorded a high of 100°F, or higher, for 15 consecutive days this July (7/13/23 to 7/27/23). The station is about three miles from the Victory Trailhead at Ahmanson Ranch.
After the Ahmanson Blue Oak in East Las Virgenes Canyon died this Winter, I started to search for another blue oak (Quercus douglasii) in Upper Las Virgenes Canyon Open Space Preserve (aka Ahmanson Ranch). Blue oaks are rare at the southern limit of their range, but I was hopeful that if there was one blue oak at Ahmanson, there might be another.
Typically, blue oak leaves are noticeably different than valley oak leaves. The Jepson eFlora describes the leaf margins of blue oak as being more or less entire, wavy, or more or less lobed. The leaves of the Ahmanson Blue Oak fit this description. Valley oak leaves are usually much more deeply lobed and readily identified.
Recently, while on a run, I noticed an unusual oak near the top of a service road on the western margin of Lasky Mesa. Its leaves are not deeply-lobed and are a bit more dusky than the usual valley oak leaf. But the tree doesn’t look quite the same as the Ahmanson Blue Oak. One difference is that the shape of the leaves is not as uniform as those of the Ahmanson Blue Oak. This might be due to the wet 2022-2023 rain season and the flourish of leaves that resulted. And, as with the Ahmanson Blue Oak, this oak was burned in the 2018 Woolsey Fire, and its trunk is partially hollow.
Based on its leaves, the “West Lasky Mesa Oak” could be a blue oak, blue oak hybrid, or valley oak hybrid. A 2002 study of a mixed stand of blue and valley oaks found that appearance can be misleading. When DNA tested, four of the five hybrid-appearing oaks in the study were not classified as hybrids. Of the four trees deemed most likely to be hybrids, only one oak was intermediate in appearance.
Although it seems unlikely this tree would have been overlooked, I could find no specific reference to the oak in the various studies and surveys done of Ahmanson Ranch. Please get in touch with me if you can provide additional information about this tree or how a DNA analysis can be arranged.
An unusually wet rain season not only increases the population of many wildflowers, it can produce wildflowers not usually seen in an area.
The Farewell to Spring (Clarkia amoena) pictured above was one of very small population found in Upper Las Virgenes Canyon Open Space Preserve (aka Ahmanson Ranch) in June 2023. The California native is much more common in the Bay Area and coastal Northern California. It probably found its way to Ahmanson by way of a local garden.