Aliso: A Journal of Systematic and Evolutionary Botany Volume 18 | Issue 2 Article 15 1999 Vascular flora of the Liebre Mountains, western Transverse Ranges, California Steve Boyd Rancho Santa Ana Botanic Garden Follow this and additional works at: http://scholarship.claremont.edu/aliso Part of the Botany Commons Recommended Citation Boyd, Steve (1999) "Vascular flora of the Liebre Mountains, western Transverse Ranges, California," Aliso: A Journal of Systematic and Evolutionary Botany: Vol. 18: Iss. 2, Article 15. Available at: http://scholarship.claremont.edu/aliso/vol18/iss2/15 Aliso, 18(2), pp. 93-139 © 1999, by The Rancho Santa Ana Botanic Garden, Claremont, CA 91711-3157 VASCULAR FLORA OF THE LIEBRE MOUNTAINS, WESTERN TRANSVERSE RANGES, CALIFORNIA STEVE BOYD Rancho Santa Ana Botanic Garden 1500 N. College Avenue Claremont, Calif. 91711 ABSTRACT The Liebre Mountains form a discrete unit of the Transverse Ranges of southern California. Geo­ graphically, the range is transitional to the San Gabriel Mountains, Inner Coast Ranges, Tehachapi Mountains, and Mojave Desert. A total of 1010 vascular plant taxa was recorded from the range, representing 104 families and 400 genera. The ratio of native vs. nonnative elements of the flora is 4:1, similar to that documented in other areas of cismontane southern California. The range is note­ worthy for the diversity of Quercus and oak-dominated vegetation. A total of 32 sensitive plant taxa (rare, threatened or endangered) was recorded from the range. Key words: Liebre Mountains, Transverse Ranges, southern California, flora, sensitive plants. INTRODUCTION belt and Peirson's (1935) handbook of trees and shrubs. Published documentation of the San Bernar­ The Transverse Ranges are one of southern Califor­ dino Mountains is little better, limited to Parish's nia's most prominent physiographic features. In con­ (1917) enumeration of the pteridophytes and sper­ trast to California's other principal cordillera-the Si­ matophytes and McBride et al.'s (1975) checklist for erra Nevada, Coast Ranges, and Peninsular Ranges­ the montane coniferous forest. By far the best-docu­ which are oriented north-south, the Transverse Ranges mented element of the Transverse Ranges has been the trend east-west. East-west trending ranges are uncom­ Santa Monica Mountains, which have been compre­ mon in North America, and geologic mechanisms re­ hensively covered by Raven et al. (1986). While the sponsible for the anomalous orientation of California's body of floristic literature for the Transverse Ranges Transverse Ranges are not yet fully understood (Norris is certainly augmented by more narrowly focused local and Webb 1990). Major units of the Transverse Ranges studies (e.g., Derby and Wilson 1978, 1979; Lewis and include, from east to west, the Little San Bernardino, San Bernardino, San Gabriel, Santa Monica, Liebre, Gause 1966; Muns 1984, 1985a, 1985b, 1986, 1992, Santa Susana, Topatopa, Pine Mountain, and Santa 1994; Parish 1890; Sawyer 1987; Swinney 1994) and Ynez ranges. Technically, this enumeration should in­ unpublished technical reports and dissertations (Boyd clude the northern group of Channel Islands, which et al. 1993; Krantz 1994; Mistretta 1995; Robinson are geologically an extension of the Santa Monica 1953; Thome 1971-1973), many segments of the Mountains. The Transverse Ranges cover a linear dis­ range remain virtual floristic terra incognita. tance of nearly 520 km (320 mi) between their western The threat to southern California's native flora from end at Point Arguello near Santa Barbara and their urbanization, agriculture, pollution, habitat fragmen­ eastern terminus in the Eagle Mountains near Desert tation, and invasive exotic taxa is pervasive and grow­ Center (Sharp 1972; Norris and Webb 1990). Physical ing. Regions such as the Transverse Ranges contain breaks between the component ranges are often ob­ large tracts of natural habitat that are biologically di­ scure and a rather diverse array of names has been verse, relatively intact ecologically, and mostly admin­ applied to various configurations, particularly in the istered in public trust; these areas are vital for meeting western portion where circumscription of physiograph­ societal goals of preserving California's natural heri­ ic units is complicated by convergence of the Teha­ tage. A critical component of any strategy for man­ chapi and Inner Coast ranges. aging regional biological diversity is developing a Although the Transverse Ranges border the Los An­ baseline account of the resources being managed. Pres­ geles Basin, California's most densely populated re­ ently, work is ongoing to provide comprehensive doc­ gion, and have been the subject of considerable botan­ umentation for both the San Gabriel Mountains (0. ical exploration over the years, published floristic ac­ Mistretta, pers. comm.) and San Bernardino Mountains counts of the component ranges are surprisingly (A. Sanders, pers. comm.). In this paper, I present a scarce. Broad-scale floristic reports for the San Gabriel preliminary floristic account of another important seg­ Mountains include Johnston's (1919) flora of the pine ment of the Transverse Ranges, the Liebre Mountains 94 Boyd ALISO 118° 20' 00" Legend c:J l.lebre Mtno Study Area Antelope Valley -- Roadways Waterways - Aqueduct -- Streams -Lakes N A Fig. 1. Map of the Liebre Mountains study area and vicinity indicating major roads, drainages, and selected peaks and ridge systems. region. The study includes the results fieldwork con­ mately 1630 km2 ( 613 mF), with elevation ranging be­ ducted by myself and/or Timothy S. Ross, with various tween 1764 m (5788 ft) on Burnt Peak and 294 m (965 associates, as well as review of collections housed in ft) where the Santa Clara River crosses Interstate 5. the herbarium of Rancho Santa Ana Botanic Garden Physiography of the Liebre Mountains region is (RSA-POM) and elsewhere. strongly controlled by two of Southern California's major fault systems: the San Andreas on the north and PHYSICAL SETTING northeast, and the San Gabriel on the west and south (Dibblee 1982). The eastern boundary of the range, Physiography and its general separation from the San Gabriel Moun­ The Liebre Mountains represent the easternmost end tains, is defined by the Soledad Fault. The range can of what is referred to collectively as the Western Trans­ be generally divided into two physiographically and verse Ranges (Hickman 1993), and they occupy a tran­ geologically discrete parts; the rugged, mountainous sitional position between the Santa Susana, Topatopa, north and northeastern section, and a lower area of and Pine Mountain ranges to the west and San Gabriel rolling hills and small erosional valleys in the west and Range to the east. The northern base of the Liebre south (Dibblee 1982). Mountains defines the southwestern border of the Mo­ Portal Ridge (including Ritter Ridge), separates An­ jave Desert. As circumscribed here, the range is a telope Valley, the westernmost end of the Mojave De­ roughly triangular area bounded by the Santa Clara Riv­ sert, from the rift zone of the San Andreas Fault. The er on the south and southeast, California Aqueduct steep escarpments of this narrow, northwest-trending along the north and northeast, and Interstate 5 along the ridge system contrast sharply with the relatively gentle west (Fig. 1). The study area encompasses approxi- relief along its crest. At its northwest end, the ridge is VOLUME 18, NUMBER 2 Liebre Mountains Flora 95 dissected by several drainages originating on the AVERAGE PRECIPITATION 1948-1995 northern flanks of Liebre and Sawmill mountains, in­ 60~--------------------------------------. cluding Tentrock, Horse Camp, Cow Spring, and Kings canyons. From Kings Canyon southeastward, 50 the crest of Portal Ridge continues unbroken to its e southern terminus at Ritter Ridge. Drainage from the !. 40 northern flank of Portal Ridge is northeastward into c ~ 30 the Mojave Desert. The shorter, steeper drainages of ..Ill the southern flank empty into the San Andreas Fault D. 1l 20 rift. .. D. The massive San Andreas rift is characterized by a 1 0 series of deep, elongate valleys separated from each other by low divides. From northwest to southeast 0 z ct ct > z ...I these include Oakdale Canyon, Oakgrove Canyon, < < :::> :::> ...,< ~ ::::;; ~ ::::;; ..., ..., ~ ~ 8 § ~ Pine Canyon, Leona Valley, and Anaverde Valley. The Fig. 2. Graph of average monthly precipitation for Sandberg southern edge of the rift zone is marked by another WSMO (located at ca. 34.75°N 118.730W, elev. ca. 1376 m.) show­ series of steep escarpments comprising the Liebre­ ing typical Mediterranean-climate pattern of winter rain and summer Sawmill-Sierra Pelona crest. These relatively narrow, drought. Source WWW.Worldclimate.com. elongate ridges, like Portal Ridge to the north, are characterized by extensive areas of gentle topography Geology across their summits. To the south of the Liebre-Sawmill-Sierra Pelona The Liebre Mountains region is geologically com­ crest lies the body of the mountainous portion of the plex (Jennings and Strand 1969). An excellent, de­ range. Topography is characterized by steep, rugged tailed geologic overview of the range is provided by ridges and narrow, winding canyons. Important topo­ Dibblee (1982), and I will present only a brief synopsis graphic features within this area include Del Sur here. The Liebre-Sawmill-Sierra Pelona crest and ad­ jacent uplands are eroded largely from pre-Cenozoic Ridge, Jupiter Mountain, Tule Ridge, Red