FLORA OF TINAJAS AltAS, ARIZONA—A CENtuRY OF BOTANICAL FORAys AND FORty THOusAND YEARS OF Neotoma CHRONICLES Richard Stephen Felger Thomas R. Van Devender Herbarium, University of Arizona Sky Island Alliance, P.O. Box 41165 Tucson, Arizona 85721, U.S.A. and Tucson, Arizona 85717, U.S.A. and Sky Island Alliance, P.O. Box 41165 Herbarium, University of Arizona Tucson, Arizona 85717, U.S.A. Tucson, Arizona 85721, U.S.A. [email protected] [email protected] Bill Broyles Jim Malusa Southwest Center School of Natural Resources and the Environment University of Arizona University of Arizona Tucson, Arizona 85721, U.S.A. Tucson, Arizona 85721, U.S.A. [email protected] ABSTRACT This flora of the vascular plants of the Tinajas Altas region, within the Lower Colorado Valley subdivision of the Sonoran Desert of southwestern Arizona, includes the present-day species as well as fossils recovered from packrat middens. The vegetation and flora are dynamic, changing even now, and have changed dramatically during the past millennia, along with shifting climate and human presences. This is the first publication for any region of a comprehensive temporal flora and spans more than 43,000 years of plants inadvertently collected and curated by packrats (Neotoma spp.) and more recently by botanists. We document a present-day flora of 227 species in 175 genera and 46 families. We also document at least 119 species in 96 genera and 36 families from the fossil record and among these fossils at least 28 species in 17 genera and 6 families are no longer present in the region. The most diverse families, present-day and fossil taxa, are Asteraceae, Poaceae, Boraginaceae, Cactaceae, Brassicaceae, Fabaceae, Solanaceae, Euphorbiaceae, Polygonaceae, and Nyctaginaceae. The most diverse genera are Cryptantha, Ambrosia, and Eriogonum. There are 12 non-native species in the flora, representing only 5.3% of the modern flora, but only Sahara mustard (Brassica tournefortii) and Arabian grass (Schismus arabicus) are likely to negatively impact the native plants. The famous waterholes, the Tinajas Altas, were critical for desert travelers and prehistoric people. The Tinajas Altas Mountains, in one of the most arid parts of North America, have one of the richest fossil records for Ice Age plants in the world. The radiocarbon-dated plant assemblages provide a detailed record of dramatic changes in geographic ranges of spe- cies and the succession from Ice Age woodlands to modern desertscrub. Prior to 11,000 years ago in the middle and late Wisconsin, Ice Age woodlands with single-leaf pinyon (Pinus monophylla), California juniper (Juniperus californica), Utah juniper (Juniperus osteosperma), Sonoran scrub oak (Quercus turbinella), and Joshua tree (Yucca brevifolia) were at Tinajas Altas and elsewhere in Sonoran Desert lowlands. The earliest known creosotebush (Larrea divaricata) in North America, 18,000 years before present, from a Tinajas Altas midden, was already the modern tetraploid Sonoran Desert race. The Tinajas Altas region encompasses 80,000 acres (32,375 hectares) adjoining the western margin of the Cabeza Prieta National Wildlife Refuge and is within the Barry M. Goldwater Range. Scientific, cultural, and aesthetic values dictate that the Tinajas Altas should receive increased attention and protection. RESUMEN El presente reporte de la flora de las plantas vasculares de la región de las Tinajas Altas en el Desierto Sonorense del suroes- te de Arizona incluye tanto las especies actuales como especies fósiles conservadas en depósitos antiguos de ratas de campo (Neotoma spp.). Actualmente la flora y la vegetación son dinámicas y siguen modificándose, pero en el último milenio los cambios han sido dramáticamente influenciados por el clima cambiante y la presencia humana. Esta es la primera docu- mentación en cualquier región de una flora integral que abarca más de 43,000 años de plantas inadvertidamente colectadas y preservadas por las ratas de campo y en época reciente por los botánicos. Aquí documentamos la presente flora consisten- te en 227 especies de 175 géneros y 46 familias. Asimismo documentamos al menos 119 especies de 96 géneros y 36 familias J. Bot. Res. Inst. Texas 6(1): 157 – 257. 2012 158 Journal of the Botanical Research Institute of Texas 6(1) como fósiles, de los cuales al menos 28 especies, 17 géneros y 6 familias ya no existen en el área. Las familias más diversas, tanto actuales como fósiles, son Asteraceae, Poaceae, Boraginaceae, Cactaceae, Brassicaceae, Fabaceae, Solanaceae, Euphor- biaceae, Polygonaceae y Nyctaginaceae. Los géneros más diversos son Cryptantha, Ambrosia y Eriogonum. La flora incluye 12 especies exóticas, que representan tan sólo el 5.3% de la flora moderna, pero sólo la mostaza del Sahara (Brassica tourne- fortii) y el zacate árabe (Schismus arabicus) probablemente tendrán un impacto negativo en las plantas nativas. Estas famosas tinajas eran una fuente de agua indispensable para los viajeros del desierto y los habitantes prehistóricos. La Sierra de las Tinajas Altas ubicada en una de las regiones más áridas de Norteamérica tiene uno de los registros fósiles de plantas más diversos de la Edad de Hielo del mundo. Las plantas datadas con radiocarbono muestran un registro detallado sobre cam- bios dramáticos en los rangos geográficos de especies y sucesiones ecológicas desde los bosques de la Edad de Hielo al ma- torral desértico moderno. Los bosques de la Edad de Hielo con Pinus monophylla, Juniperus californica, J. osteosperma, Quercus turbinella y Yucca brevifolia se encontraban en las Tinajas Altas y en otras regiones bajas del Desierto Sonorense hace 11,000 años durante el período Wisconsin Medio y el Wisconsin Tardío. El registro más antiguo de gobernadora (Larrea divaricata) en Norteamérica, 18,000 años antes del presente, de un depósito de rata de campo, representa la raza tetraploide moderna del Desierto Sonorense. La región de las Tinajas Altas formó parte del refugio de vida silvestre Cabeza Prieta Na- tional Wildlife Refuge y actualmente del Barry M. Goldwater Range. Los valores científicos, culturales y estéticos sugieren que las Tinajas Altas deben recibir mayor atención y protección. INTRODUCTION The Tinajas Altas, or High Tanks, are famous through history and were utilized for millennia by Native Amer- icans (Broyles et al. 2012). If you were traveling across the Camino del Diablo, part of the old Yuma-Caborca trail, you would head for the Tinajas Altas (Fig. 1). Sometimes the lower tanks would be dry and getting to the upper tanks could be daunting, and some travelers did not know about the upper pools or were not able to reach them. Missing the tinajas and their water could spell death to desert travelers. The importance of Tinajas Altas grew during the California gold rush of the mid-nineteenth century and by the end of that century they became a focus for desert research by the likes of WJ McGee and Edgar Mearns. Mearns (1907: 122) wrote, “This important station is at the east base of the [mountains], beside the lowest of a chain of natural rock tanks, in a steep ravine, containing an unfailing and almost inexhaustable supply of good water. The upper tanks are easily overlooked and difficult of access, which facts afford the most plausible explanation of the loss of lives of many persons whose bones and graves were thickly scattered about our camp” (Figs. 2 & 3). The Tinajas Altas Mountains are a rugged range, rising 500 meters from the desert floor of southwestern Arizona. There are no foothills, only slabs of pale Eocene granite rising abruptly at an unlikely angle of 45 de- grees (Fig. 4). Along a skyline fretted with spires and windows there are no trees or saguaros to provide scale, no sense of near or far. If you camp in a comfortable arroyo near the foot of the mountains and look to the peaks on a full-moon evening the Tinajas Altas are as brilliant as snow and as eye-popping as any great mountain (Fig. 5). The extremely arid Tinajas Altas region is situated along the Mexican border at a remote edge of the Barry M. Goldwater Range, about 70 km southeast of Yuma, Arizona (Fig. 6). The Tinajas Altas Mountains are 35 km long, trending southeast-northwest from the international border to the Gila Mountains, where the granite is rather dramatically replaced by dark schist. The Tinajas Altas site (the waterholes) is about 6.5 km north of the Mexican border and is reached by the Camino del Diablo, a graded dirt road running south from Interstate 8 and then eastward across the Lechuguilla Valley and the Cabeza Prieta National Wildlife Refuge. In spite of many visitors, the mountains and much of the adjacent valleys remain in near pristine condition, although the upper bajadas and various other areas continue to be severely impacted by illegal off-road driving and other recreational activities, and more recently by the massive construction activity of the U.S. border fence in 2008 (see Department of Homeland Security 2008). We selected the flora area because of the rich fossil and modern botanical record and because it embraces a variety of desert habitats, is a convenient biological and cultural zone (delineated by U. S. Fish and Wildlife Service) and is an area of major conservation concern. The core flora area is the 80,000 acres (32,375 hectares) of the Tinajas Altas region encompassing the Tinajas Altas Mountains from the Cipriano Pass to the Mexico border at Frontera Canyon and the south end of the Lechuguilla Valley drained northward by Coyote Wash and southward by La Jolla Wash (Fig. 7). We also include some plant records from the nearby Butler Mountains Felger et al., Flora of Tinajas Altas, Arizona 159 FIG. 1. The Gran Desierto and Camino del Diablo (Quitobaquito–Yuma portion of the Old Yuma–Caborca Trail) and surrounding regions, adapted from map in Lumholtz (1912).