Del Cabo Research Articles

SWIVI: A climate change-oriented multi-parametric framework to enhance saltwater intrusion vulnerability assessment

Saline intrusion is a phenomenon that most frequently affects coastal aquifers, reducing the quality of groundwater used for human consumption. An approach to address this problem is from a vulnerability perspective. Based on the ESCA framework, we propose a vulnerability model that includes internal and external indicators of social, environmental, and hydrogeological components coupled with groundwater modeling data to forecast vulnerability to seawater intrusion in a coastal aquifer. The indicators selected were grouped and weighted after a K-means and Principal Components analysis. As a case study, we selected the San José del Cabo aquifer located in the state of Baja California Sur, Mexico, which presents a deficit in its availability and strong pressures resulting from population and industrial growth. The results indicate for the year 2019 conditions of high vulnerability in the coastal zone and in the San José del Cabo stream. By the year 2040, the very high vulnerability areas will extend inland. The model presented made it possible to accurately define the vulnerability due to saline intrusion in two periods, allowing the generation of actions in the short-medium term to limit its advance. The developed framework allowed the determination and prediction of vulnerability due to saline intrusion in a coastal aquifer system impacted by climate change and overexploitation.

Ancient Rock Paintings at Region del Cabo-BCS, Mexico: An Analytical Study

This study focused on the examination of six rock pictorial panels and a solitary figure from four archaeological sites in the Sierra de las Cacachilas (Sector A) in the Region del Cabo, Baja California Sur, Mexico. Scanning Electron Microscopy-energy dispersive X-ray spectroscopy was utilized to analyze tiny samples of the pictorial layers, patina, rocky supports, and natural pigments. The concentrations of C, Mg, Al, Si, P, S, K, Ca, Cr, Ti, Mn, and Fe were subjected to statistical methods and the samples were divided into various clusters. Iron and calcium compounds appear to be the primary constituents of the pictorial layers. The red pigment spectra obtained through Fourier-transform infrared spectroscopy revealed the presence of inorganic compounds and the likelihood of a flora-based composite as the binding agent. The minerals identified through X-ray diffraction in the rocky supports were determined to be intrusive igneous rocks. These findings are significant for the conservation and preservation of the artwork in the Sierra de las Cacachilas.

Turismo y planeación urbana en San José del Cabo, Baja California Sur (México)

The localities from their origin face a series of events that can condition them to their future configuration. San Jose del Cabo, in the Mexican state of Baja California Sur, emerged in colonial times as the site of a mission founded by the religious order of the Society of Jesus. Since the eighties of the last century, it became a place where public policies were applied in the field of tourism, an aspect that gave rise to a great physical growth of the urban place due to the social growth of the population to become a focus of attraction for immigrants attracted by the jobs associated with leisure activity. The objective of this essay is to provide an explanation of the urban evolution of San José del Cabo through an analysis of different documentary sources, such as bibliography, reports and urban planning instruments prepared by government agencies.

Migratory Behavior of an Eastern North Pacific Gray Whale From Baja California Sur to Chirikov Basin, Alaska

Eastern gray whales undertake annual migrations between summer feeding grounds in the Bering and Chukchi Seas and winter breeding and calving lagoons in the west coast of Baja California, Mexico. On February 12, 2017, three adult gray whales were sighted at San José del Cabo, Mexico, in which one individual, named “María,” was tagged using a satellite telemetry transmitter (PTT). The PTT stopped the signal on July 11, 2017. María traveled 11,387 km during 149 days from San José del Cabo to the Chirikov Basin. The migration route was aligned close to the coastline (<23 km) from February to April. After passing Kodiak Island in May, María started traveling far away from the coastline (>70 km) into the Bering Sea, including the Chirikov Basin. During March, April, and May, María traveled long distances at relatively high speeds, in contrast to the lower speed during February, early March, and the arrival time to the feeding areas in May, June, and July. The total distance traveled by María during its migration from Ojo de Liebre Lagoon to the Chirikov Basin was 8,863 km during 61.5 days with an average speed of 5.5 km h–1; this excludes the 14 days and 591 km that María spent feeding on the coast of Kodiak Island in late April. The information provided by this tagged whale documents a single whales’ migration, which is consistent with previous studies and constitutes the most complete northbound reported migration of an eastern gray whale.

Efectos de los ciclones tropicales sobre la cubierta vegetal de la cuenca baja y estero San José del Cabo, Baja California Sur, México

Introduction: Tropical hurricanes modify composition and structure of ecosystems. Objective: To analyze the impact of tropical hurricanes on the recovery and resilience of vegetation cover.Materials and methods: The resilience of the lower basin and estuary of San Jose del Cabo was evaluated by studying the impact of 11 tropical hurricanes (2013-2017) on the vegetation cover. Landsat images were analyzed for each event and two SPOT-6 images for the Hurricane Lidia. The areas of gain, stability, loss and recovery of vegetation types were estimated based on the analysis of changes in the Normalized Difference Vegetation Index (NDVI).Results and discussion: Average stability of vegetation cover was 90 %; however, in the case of hurricane Odile (2014) and Lidia (2017), stability decreased considerably, with a loss of 35.4 and 20.5 %, respectively, being the perennial herbaceous vegetation the most affected. One year after Odile and Lidia, recovery was 8.4 % and 25.4 %, respectively; the most recovered vegetation type was reed-tree. The analysis of SPOT-6 images allowed the detailed observation of Lidia's effect on palm grove. The main cause of its loss was runoff from the stream, which favored the growth of invasive species (Arundo donax L. and Tamarix sp.); furthermore, it was estimated that 1.4 ha were deforested, and an area of 20 ha affected by fire in 2017.Conclusion: Vegetation is resilient to tropical hurricanes; however, events that provide more than 50 % of annual precipitation decrease the capacity of vegetation to recover.

Groundwater Flow Model and Statistical Comparisons Used in Sustainability of Aquifers in Arid Regions

Groundwater provides the most important of the water resources used in the maintenance of communities in arid and semi-arid regions. In these areas, the usage of deep wells with motorized pumps in combination with the lack of effective regulatory policies and high human population growth (increase the water demand) impact the quality of the groundwater. This is especially the case for the San José del Cabo aquifer, in Baja California Sur. In the present study the groundwater flow system is analyzed in order to recognize the impact from variations in groundwater extraction and recharge on the phreatic levels and discharge values. In order to achieve this goal, a groundwater model was generated using the MODFLOW program. Different scenarios of extraction and recharge were calculated, based on different estimations of population growth. All the scenarios result in decreasing groundwater levels. As an important result, a relationship between the phreatic level and the extraction volume was found for the middle zone of the aquifer, where an average annual decrease of 0.5 m was observed from every 5 × 106 m3 additional extraction volume. This zone is up to three times more susceptible to changes in extraction values than the southern zone. As the results show, the San José del Cabo aquifer is in a fragile state where an increment in extraction is not an option without the use of remediation technics or new sources for water supply.

Sustentabilidad en el área turística Estero San José del Cabo, México

La Reserva Ecológica Estatal Estero de San José del Cabo (REEESJC) es un área natural protegida (ANP) en el municipio de Los Cabos, un destino turístico importante de México. El objetivo de esta investigación es analizar la percepción y opinión de las autoridades que administran el área, así como los grupos de interés (Líderes comunitarios y empresarios) sobre la sustentabilidad del ANP. Durante 2016 se aplicó una encuesta con variables cualitativas y cuantitativas. Los encuestados perciben como principal problema la falta de conocimiento del plan de manejo, por parte de los actores locales. Opinan que las estrategias prioritarias de manejo deben ser la conservación y vigilancia. Las autoridades y grupos de interés que se encargan de la planeación de las actividades turísticas en el área de estudio muestran un desconocimiento sistemático de información que les permitiría proponer acciones de conservación eficaces frente al reto de la sustentabilidad del ANP.

Evolución estratigráfica de la cuenca Los Barriles, Baja California Sur, México

The Los Barriles basin, located north of the San José del Cabo basin, is part of the Gulf Extensional Province. It is a half graben bounded by the Los Barriles fault system on its western side. Our study confirms that this system is not part of the San José del Cabo fault but an independent structure. The basin fill includes three stratigraphic sequences: SE 1, SE 2, and SE 3. Los Barriles and Trinidad Formations constitute SE 1. The Los Barriles Formation is in contact with the marginal fault and on the eastern margin it rests unconformably upon the plutonic and meta- morphic basement. The unit is composed of conglomerate and sandstone formed in alluvial fans. The marine Trinidad Formation is composed of sandstone and mudstone. Both formations interfinger and constitute fan deltas without foresets, suggesting rapid subsidence along the Los Barriles fault. Calcareous nannofossils in SE 1 point toward an age in the nannofossil zone NN11 (Late Tortonian-Messinian). Thus, faulting and subsidence occurred since the late Miocene, indicating that the Los Barriles fault system is older than the San José del Cabo fault, which had been activated during the Pliocene. The Refugio Formation (SE 2) rests unconformably on the Trinidad Formation; it consists of fossiliferous sandstone and conglomerate originated in a shallow marine coastal set- ting. Laterally, it interfingers with younger portions of the Los Barriles Formation, forming a fan delta setting of probable Pliocene age. The El Chorro Formation unconformably covers all older units and, locally, even Los Barriles fault system. It comprises sandstone and conglomer- ate formed in an alluvial fan depositional environment. These deposits interfinger towards the present coastline with fossiliferous sandstone and conglomerate formed during the last interglacial period, representing SE 3.

Hydrogeochemical characterization of the thermal springs in northeastern of Los Cabos Block, Baja California Sur, México.

The existence of hot springs in the northeastern part of Los Cabos Baja California Sur (BCS), is known from pre-Hispanic times, but their hydrochemical composition had not been previously described. Several springs are located within the watershed of Santiago, and the objective of this study was to define the hydrogeochemical composition of the thermal springs and to characterize the geothermal reservoir. A total of 16 water samples were taken in 11 geothermal manifestations under dry (June 2014) and humid (March 2015) conditions. A geothermal system of low enthalpy and low mineralization was found along the San José del Cabo Fault (FSJC), with an average salinity (TDS) of 261mg/L and an alkaline pH (8.5-9.5). The hydrogeochemical composition corresponds to the sodium-bicarbonate type, and geothermometers (silica and Na-K) indicate temperatures ranging from 70 to 115°C for the deep thermal reservoir in conditions of equilibrium. The thermal springs with these hydrogeochemical characteristics differ in respect to the hydrochemical composition of the springs, formally described on several sites of BCS. Br/Cl and B/Cl ratios as well as the enrichment factor (EF) indicate that rainwater with a seawater component represents the source of the thermal spring water. In the springs, a mixture between thermal water and surface water is observed, combined with a relatively deep water circulation, allowing a calcium-sodium exchange, according to the host rock geochemistry. The higher temperatures found at some hot springs are related to the main trace of the San José del Cabo Fault.

Late Pleistocene-Holocene alluvial stratigraphy of southern Baja California, Mexico

Abstract A late Pleistocene to Holocene alluvial stratigraphy has been established for the basins of La Paz and San Jose del Cabo, in the southern tip of the Baja California peninsula, Mexico. Six discrete alluvial units (Qt1 through Qt6) were differentiated across the region using a combination of geomorphologic mapping, sedimentological analysis, and soil development. These criteria were supported using radiocarbon, optically stimulated luminescence and cosmogenic depth-profile geochronology. Major aggradation started shortly after ∼70 ka (Qt2), and buildup of the main depositional units ended at ∼10 ka (Qt4). After deposition of Qt4, increasing regional incision of older units and the progressive development of a channelized alluvial landscape coincide with deposition of Qt5 and Qt6 units in a second, incisional phase. All units consist of multiple 1–3 m thick alluvial packages deposited as upper-flow stage beds that represent individual storms. Main aggradational units (Qt2-Qt4) occurred across broad (>2 km) channels in the form of sheetflood deposition while incisional stage deposits are confined to channels of ∼0.5–2 km width. Continuous deposition inside the thicker (>10 m) pre-Qt5 units is demonstrated by closely spaced dates in vertical profiles. In a few places, disconformities between these major units are nevertheless evident and indicated by partly eroded buried soils. The described units feature sedimentological traits similar to historical deposits formed by large tropical cyclone events, but also include characteristics of upper-regime flow sedimentation not shown by historical sediments, like long (>10 m) wavelength antidunes and transverse ribs. We interpret the whole sequence as indicating discrete periods during the late Pleistocene and Holocene when climatic conditions allowed larger and more frequent tropical cyclone events than those observed historically. These discrete periods are associated with times when insolation at the tropics was higher than the present-day conditions, determined by precessional cycles, and modulated by the presence of El Nino-like conditions along the tropical and northeastern Pacific. The southern Baja California alluvial record is the first to document a precession-driven alluvial chronology for the region, and it constitutes a strong benchmark for discrimination of direct tropical influence on any other alluvial record in southwestern North America.

Opinión pública y percepción sobre la conservación de la reserva ecológica estatal Estero San José del Cabo y su zona de influencia / Public opinion and perception on the conservation of Estero San José del Cabo state ecological reserve

El objetivo de esta investigación es conocer el grado de conocimiento de la población que vive y/o trabaja en la zona de influencia del Estero San José del Cabo sobre la conservación del área, así como su opinión y percepción sobre el desempeño y trabajo del gobierno sobre acciones para la conservación. Durante 2014 aplicó una encuesta cualitativa y cuantitativa. Los resultados muestran que 93% conoce lo que es un ANP, 77% percibe beneficios al vivir/trabajar cerca de un ANP, solo 38% conoce la existencia del programa de manejo, 36% percibe que sus actividades económicas y sociales fueron afectadas tras la creación del ANP, 23% percibe mejora en oportunidades de empleo; 74% opina que la vigilancia de los administradores es nula, 65% de ellos perciben que no se invierten recursos financieros, humanos e infraestructura para el manejo de la reserva. Finalmente 52% opinan que la aplicación de instrumentos normativos y sanciones administrativas es nula.

Miocene detachment faulting predating EPR propagation: Southern Baja California

AbstractAt the southern tip of the Baja California peninsula, we characterize the onshore structures and kinematics associated with crustal necking leading up to the Pliocene breakup and early East Pacific Rise seafloor spreading. From a combination of tectonic field investigations, K‐Ar and cosmogenic isotope dating and geomorphology, we propose that the Los Cabos block represents the exhumed footwall of a major detachment fault. This north trending detachment fault is marked by a conspicuous low‐dipping brittle‐ductile shear zone showing a finite displacement with top to the SE ending to the ESE. This major feature is associated with fluid circulations which led to rejuvenation of the deformed Cretaceous magmatic rocks at a maximum of 17.5 Ma. The detachment footwall displays kilometer‐scale corrugations controlling the present‐day drainage pattern. This major detachment is synchronous with the development of the San José del Cabo Basin where syntectonic sedimentation took place from the middle Miocene to probably the early Pliocene. We propose that this seaward dipping detachment fault accommodates the proximal crustal necking of the Baja California passive margin, which predates the onset of formation of the East Pacific Rise spreading axis in the Cabo‐Puerto Vallarta segment. Our data illustrate an apparent anticlockwise rotation of the stretching direction in Baja California Sur from ~17 Ma to the Pliocene.

Fronteira: Caminhos do Contrabandista

O presente trabalho tem como objetivo revelar, através de contos literários de autores do Rio Grande do Sul e do Uruguai, uma visão do perfil do homem contrabandista, explicitando articulações que permitem ao público leitor ter diferentes versões desse personagem que, para uns, é considerado herói e, para outros, bandido. Para atingir tal proposta, serão examinados os contos “Contrabandistas”, de João Simões Lopes Neto; “Contos IV” e “Nossa Senhora Aparecida”, de Aldyr Garcia Schlee; “Contrabandistas”, de Julián Murguía; “Contrabando”, de Darcy Azambuja; “Cerrazón” e “Renuncia del comisario Portela y del cabo Lapuente”, de José Monegal, que enfocam a vida dos moradores da fronteira, espaço por onde transitava o comércio ilícito. Para análise dos textos, tomam-se como referenciais pesquisas de Guilhermino César, Adriana Dorfman, Léa Masina e Mariana Flores da Cunha Thompson Flores, críticos de diferentes áreas que tomam a literatura para aprofundar estudos sobre o contrabando na fronteira. Esta pesquisa permitirá detectar motivos que levavam os indivíduos a realizar contrabandos, bem como as consequências dos seus atos ilícitos. Isso nos leva a refletir sobre o caráter desses sujeitos. Seriam eles heróis ou bandidos?

Control social en el asentamiento colonial Nuestra Señora Santa María de los Remedios del Cabo de la Vela

The colonial settlement for the extraction of pearls, Nuestra Senora Santa Maria de los Remedios del Cabo de la Vela was founded during the first half of the 16thXVI century. The study has focused to determine if segregationist practices occurred between contact groups in this type of Spanish location. Although the Spanish Crown imposed policies of spatial division and control of different socio-cultural groups within the colony, preliminary results suggest that these not always became effective.

Entomological Indicators to Assess LarvalAedes aegypti1(Linnaeus, 1762) Control in Baja California Sur, México

Abstract. Aedes aegypti (Linnaeus, 1762) is the mosquito species responsible for transmission of yellow and dengue fevers. Different strategies are used worldwide to reduce its abundance, but effectiveness is not well understood. The aim of this work was to evaluate the effectiveness of chemical control of larvae of this species using different indices before and after application at three locations in Baja California Sur, Mexico. The presence of Ae. aegypti larvae was evaluated by three larval indices: house index, container index, and Breteau index at three locations at Cabo San Lucas, La Paz, and San Jose del Cabo during 3 years (2011–2013) before and after chemical control and reduction of potential breeding sites by the Secretaria de Salud (health department of Baja California Sur). The data showed significant statistical differences (p < 0.001) in the relative abundance of Ae. aegypti larvae before and after applying larvicide (Temephos®) and by removing water containers where mosquitoes reproduce, ...

A transitional skunk, Buisnictis metabatos sp. nov. (Mephitidae, Carnivora), from Baja California Sur and the role of southern refugia in skunk evolution

Fossil records for basal New World skunks (subfamily Mephitinae) have been slowly but steadily increasing in recent years. Fossils for both living and extinct genera are now dense enough that actual evolutionary steps leading to living clades are beginning to be resolvable. We document a new species of the extinct, transitional genera Buisnictis, B. metabatos sp. nov., from Early Pliocene San José del Cabo Basin, Baja California Sur, México. B. metabatos possesses a combination of primitive and derived features, including a broadened P4 protocone shelf, a notch anterior to the m1 entoconid, and relatively unexpanded M1 lingual cingulum. It thus fills in yet another morphological gap and it is at a basal position within or just outside of the living skunk clade. Although current records are still far too scattered to resolve detailed zoogeographical patterns, we are in a position to speculate that since the Early Pliocene, southern North America and Central America have acted as a refugium for skunks. As a basal skunk, Buisnictis metabatos probably gave rise to the modern crown clade. There is evidence to suggest that both spotted skunks (Spilogale) and hog-nosed skunks (Conepatus) had their centres of diversification in Mexico or Central America. The only exception may be the striped and hooded skunks (Mephitis), which have a more northerly distribution.http://zoobank.org/urn:lsid:zoobank.org:pub:4B6D618A-A25D-4855-AAD5-AE93DFE900C7

Flocking Behaviour Does Not Favour High Chewing Lice Load in Shorebirds

Flocking behaviour does not favour high chewing lice load in shorebirds.As shorebirds show a high variability in the flocking behaviour among species from solitary ones to species forming flocks of hundreds of individuals, they offer a good opportunity to test if the proximity of individuals in highly gregarious species increases the risk of horizontal ectoparasite transmission in comparison with solitary species. We investigate whether there exists a higher ectoparasite load in gregarious shorebirds compared to solitary ones at Salinas del Cabo de Gata, Almeria, Spain. Seven species of shorebirds (Scolopacidae and Charadriidae) were captured with mist-nets during the night. Ectoparasites were estimated by means of visual examination of seven body regions and differentiated in five levels of infestation. Flock size was divided into three categories: solitary species, species forming flocks up to 99 individuals and species forming flocks of more than one hundred. Based on the application of a phylogenetic comparative method, our results show that the abundance of chewing lice is not related with flocking behaviour.

Geometry and evolution of rift-margin, normal-fault–bounded basins from gravity and geology, La Paz–Los Cabos region, Baja California Sur, Mexico

The southern end of the Baja California peninsula is cut by a north-striking, left-stepping, active, normal-fault system—the marginal fault system of the oblique-divergent plate boundary within the Gulf of California. We conducted gravity surveys across the normal-fault–bounded basins, and, along with optically stimulated luminescence dating of offset piedmont surfaces and geologic data, we estimated fault-slip rates and assessed fault patterns across basins, gaining insight into basin evolution to better understand the role of upper-crustal processes during development of an obliquely rifted plate margin. Gravity surveys across the La Paz, San Juan de los Planes, and San José del Cabo basins revealed basin depths ranging from ∼500 to 3000 m. The La Paz basin is a half graben with two smaller basins that reflect the two main east-dipping splays of the Carrizal fault. Within the San Juan de los Planes and San José del Cabo basins, there are buried faults, indicating that during the early stages of basin formation, strain was distributed across these smaller intrabasin faults prior to development of the basin-bounding faults. Slip rates coupled with basin depths suggest that the La Paz and San Juan de los Planes basins began forming ca. 2–5 Ma, overlapping in time with the formation of the main plate boundary at this latitude. The San José del Cabo basin has the greatest depth to bedrock (1.6–2.7 km), signifying that it accommodates a greater slip rate or a longer duration of slip than the other faults within this system.

Occurrence of Pyrodinium bahamense var. compressum along the southern coast of the Baja California Peninsula

As part of a continuing toxic microalgae monitoring program, 22 phytoplankton samples were collected from July to November 2010 at several sampling stations along the southern coast of the Baja California Peninsula. For the first time, the toxic dinoflagellate Pyrodinium bahamense var. compressum was found along the southeastern and southwestsern coasts of the peninsula. P. bahamense var. bahamense was first observed off San José del Cabo, which is an extension of the range of this variety. Both varieties occur as solitary cells. P. bahamense var. compressum occurred at temperatures ranging between 24.5°C and 31°C, whereas var. P.bahamense occurred at 28.5°C to 29°C, indicating its tropical and subtropical nature. Occurrence of P. bahamense var. compressum along this coastline may be related to El Niño 2009–2010.

On the native Nearctic species of the huntsman spider family Sparassidae Bertkau (Araneae)

The native Nearctic species of the family Sparassidae are revised. Eight synonymies are proposed, reducing the number of species to five: Olios schistus Chamberlin 1919, O. scepticus Chamberlin 1924 and O. positivus Chamberlin 1924 with O. peninsulanus Banks 1898; O. albinus Fox 1937 and O. foxi Roewer 1951 with O. naturalisticus Chamberlin 1924. Olios concolor Keyserling 1884 and O. pragmaticus Chamberlin 1924 are removed from the synonymy of O. fasciculatus Simon 1880 and synonymized with O. giganteus Keyserling 1884. All species currently included in the genus Olios Walckenaer 1837 are redescribed and illustrated, and new distribution records are presented. Comparisons between these species and the type species of the genus Olios, Olios argelasius (Walckenaer 1805), shows that none of them are congeneric and that true Olios does not occur in the Nearctic region. Nevertheless, the correct placement of these species in new genera will only be possible after a more thorough revision of the Nearctic and Neotropical fauna, especially that of Mexico and Central America. The Nearctic region comprises most of the North American continent, including Greenland and the northern highlands of Mexico (Udvardy 1975). To date, only thirteen Sparassidae species have been described from this region (eight from the USA and five from Northern Mexico), all assigned to the genus Olios Walckenaer 1837: Olios franklinus Walckenaer 1837, O. concolor Keyserling 1884, O. giganteus Keyserling 1884, O. peninsulanus Banks 1898, O. schistus Chamberlin 1919, O. naturalisticus Chamberlin 1924, O. positivus Cham- berlin 1924, O. scepticus Chamberlin 1924, O. pragmaticus Chamberlin 1924, O. albinus Fox 1937, O. bibranchiatus Fox 1937, O. mojavensis Fox 1937 and O. foxi Roewer 1951 (Platnick 2010). Olios franklinus, the first sparassid to be described from the Nearctic region, was proposed by Walckenaer (1837) from the USA. Nevertheless, the female type was never located and the identity of the species is considered doubtful. Olios fasciculatus was described by Simon (1880), based on a male and female from Mariposa County, California, USA. Roth (1988) examined the type series and, based on Simon's description, designated a male lectotype. Nevertheless, no females fitting the original description were found amongst those in the type series suggesting that these were added posteriorly and were not conspecific with the described male. Also, since no other Olios specimens were found in the collections from California, Roth raised the possibility that the vial was actually mislabeled. Jager & Kunz (2005) confirmed Roth's suspicions and matched the lectotype to specimens from Tanzania. Thus, the species is not native and most likely does not occur in the Nearctic region. Keyserling (1884) described O. giganteus, O. concolor and O. abnormis from New Mexico, USA. The name abnormis was preoccupied by Sparassus abnormis Blackwall 1866 and the species was given the new name Olios foxi by Roewer (1951). Olios concolor and O. giganteus were synonymized with O. fasciculatus by Banks (1893) and the latter removed from this synonymy by Roth (1988). Olios peninsulanus was described by Banks (1898), based on a male and a female from San Jose del Cabo, Baja California, Mexico. Chamberlin (1919) described O. schistus from Claremont, Los Angeles, USA, and a few years later (1924), O. naturalisticus, O. positivus, O. scepticus and O. pragmaticus from the Gulf of California (Tiburon Island, San Francisco Island, Ceralba Island, and San Lorenzo Island, respectively), Mexico. Olios pragmaticus was synonymized with O. fascicu- latus by Fox (1937) who revised the Nearctic fauna of Sparassidae and described three new species: Olios albinus, from Phoenix, Arizona, O. bibranchiatus, from Madera Canyon, Arizona, and O. mohavensis, from the Mojave desert, California. He also recorded the presence of two non native sparassid species: Heteropoda venatoria (Linnaeus 1767), a widely distributed pantropical species, and Pseudosparianthis cubana Banks 1909, originally described from Cuba, in Southwestern USA and Florida, respectively. Olios mohavensis was recently transferred to Macrinus by Rheims (2010). In this paper I present the taxonomic revision of the native Nearctic fauna of Sparassidae. All species, currently included in the genus Olios, are redescribed and illustrated. Compar- isons between these species and the type species of Olios, Olios argelasius (Walckenaer 1805), show that none of them are congeneric and that true Olios does not occur in the Nearctic region. Nevertheless, the correct placement of these species in new genera will only be possible after a more thorough revision of the Nearctic and Neotropical fauna, especially that of Mexico and Central America.