Santa Catalina Mountains Research Articles

Experiments on Treatment of Summer Cumulus Clouds

University of Arizona carried out program of cloudseeding research directed towards study of effects of silver-iodide nuclei on supercooled orographic cumuli; clouds over Santa Catalina Mountains in southeastern Arizona were studied.

Types of Pediments in the San Pedro Valley Region, Arizona

1954of Pacific Coast Geographers17 TYPES OF PEDIMENTS IN THE SAN PEDRO VALLEY REGION, ARIZONA Tuan Yi-fu University of California, Berkeley The word pediment, as first defined by McGee (1) and as used in this paper, refers to an exposed bedrock surface at the foot of the mountain front, or a rock surface covered by a layer of alluvium no thicker than the depth of the stream scour. In igneous rocks of coarse texture, the pediment may be covered only by its own regolith — i.e, the material weathered in place rather than transported alluvium. Under this definition, which excludes all postulates of an extension of the surface beneath the alluvium, the pediment is only a fragmentai feature of the arid landscape in the American Southwest in contrast to the ubiquity of alluvial fans, bahadas, and bevelled piedmont surfaces or "peripediments". There are at least two major types of pediments in the San Pedro Valley region of Arizona: 1. The narrow rock benches or embayments which fringe a broad mountain mass, and are separated from the alluvial deposits of the basin by a high-angle fault; 2. The extensively bevelled bedrock surfaces out of which the mountains appear to rise as mere residuals. The¦Santa Catalina and Huachuca pediments belong to the first type, whereas the south Dragoon and Johnny Lyon Hills pediment belong to the second. The Santa Catalina Pediments The northwest and south fronts of the Santa Catalina Mountains show narrow pediments because they have had little time to develop since the latest major uplift along the normal faults in late Tertiary or early Quaternary time (?). The morphology of these pediments can be described best in the context of their adjoining mountain fronts. (Figure 1) The south front of the Santa Catalina Mountains is composed of gneiss. It is much ravaged by erosion, and has a series of parallel canyons separated by bare, sharp-crested ridges. The northwest front is divisible into two morphologic units along the Romero and Montrose canyons. The belt occupied by these canyons marks the transitional zone between gneiss of the southern forerange and an intrusive igneous rock of distinctly granitic texture in the northern portion of the northwest front, where it is known as the Samaniego Ridge. Canyons and sharp crests are absent in the Samaniego Ridge which is rounded at the top and has long, smooth, concave slopes leading down to the foot of the mountain. It is along this granite ridge that amphitheatre-like, incipient pediments have formed. (2) Wide pediments generally do not occur along a deeply dissected mountain front, and the southern forerange off the Santa Catalina Mountains is no exception. Here, large alluvial fans appear to emerge directly from the mouths 18 Yearbook of The Association Vol. 16 Figure 1. Diagram of the northwest corner of the Santa Catalina mountains. SW SANTA CATALINJA PEDIMENT BENCH NE Pediment Bench Fan A (Mesa) Fan B Fan C Fan B Gneiss . Conglomerate beds (Tilted and deformed) Figure 2. Diagrammatic cross-section of the south front of the Santa Catalina mountains showing the relationship between the pediment benches and the alluvial fans. (Modified from Blissenbach ) 1954of Pacific Coast Geographers19 of the canyons, and the steep mountain wall seems to be in sharp contact with the aggradational slope of the fans. But this simple arrangement is deceptive and fades upon closer scrutiny. The fans have been much eroded. Blissenbach recognizes three fan levels, the highest and oldest remnants of which are isolated knolls or mesas. (3) The highest fan mesa, when projected toward the mountain front and across the fault that separates the gneiss from the alluvium, correspond in elevation to the narrow pediment benches developed on gneiss, whereas a more recent fan (fan B) still covers much of the lower gneissic surface. It is outside the scope and purpose of this paper to trace the history of the uplift of the mountain front along the fault, and the relation of the succesive fans to the pediment benches. Figure 2 summarizes a possible interpretation in diagrammatic form. The rock benches are at most only a few hundred feet wide. They have suffered much from erosion, and are best preserved in the intercanyon areas...

Rainfall Records for the Sonoran Desert

The scientific investigation of a region from the viewpoint of any branch of modern geography with its numerous ramiifications should include accurate information concerning the climatic conditions. This is particularly true for biological studies in a typically arid region such as the Sonoran Desert of southwestern Arizona, southeastern California, and northwestern Sonora. Here the rainfall, because of its relative scarcity and uncertain distribution, is undoubtedly the most important climatic factor to be considered. It has a profound influence upon the survival and distribution of the various species which constitute the flora and fauna. A record of the rainfall at the Desert Laboratory, Tucson, Arizona, has been kept since its establishment by the Carnegie Institution of Washington in 1903. The following year a raingauge was placed in the foothills of the Santa Catalina Mountains some ten miles distant from the Laboratory. Nunmerous other rainfall stations were established from time to time and were maintained for longer or shorter periods in connection with experimental projects. In 1925, however, an extensive investigation of the rainfall on the Sonoran desert area was begun. The pronounced local nature of the majority of the storms in this region made it essential that as extensive an area as practical be included in the study. Two principal lines of raingauges were established along diverging routes from Tucson and a series of gauges has lbeen concentrated on the grounds of the Laboratory and in the immediate vicinity. The approximate location of most of these rainfall stations is shown by Sykes ('31) on a map of southern Arizona and northern Sonora. Since his publication appeared additional stations have been established. Figure 1 shows the location of the stations for which data are presented in this paper. The series of gauges known as the Libertad line extends in a southwesterly direction from Tucson to Cirio Point, formerly designated as Kino Point, nine miles south of Puerto Libertad, Sonora, on the Gulf of California. The outstanding features of the topography and of the vegetation along the Libertad line have been presented by Shreve ('24). Each gauge has been located at a point which possesses some particular botanic or topographic feature. The,Camino line of gauges follows a route which leaves the Libertad line 24 miles west of Tucson. This route continues on to Ajo, 135 miles west

A Detailed Study of Desert Rainfall

It is well known that the precipitation that falls during a given rain is not uniform throughout the area covered by the storm. A desire to obtain a better knowledge of these variations in a desert climate and their possible effects on vegetation prompted this study. The only previous investigation of rainfall differences on a small area that has come to my attention is one carried out by Musson ('03) near Windsor, New South Wales. In this work 47 gauges were placed in the form of a cross i mile long and readings were taken after each shower for three months. The highest readings in this series were from 25 per cent to 30 per cent greater than the lowest readings. The author concludes that variations of 20 per cent or more may be expected in the precipitation falling on a single square acre. In August, I930, a series of 24 rain gauges was installed on the grounds of the Desert Laboratory. Sixteen were placed in four rows of four gauges each at intervals of ioo m., thus occupying a square 300 m. on a side. This square was located on the level ground immediately west of Tumamoc Hill. Eight additional gauges were placed in a straight line at i00 m. intervals from the east corner of the square toward the base of Tumamoc Hill and up its slopes to a spot 200 meters above its base (fig. i). A type of gauge was used that consisted of a galvanized iron funnel topped by a vertical collar 5 inches high, inserted through a cork in the top of a quart mason jar. An instrument of this same general type was used by Shreve ('I5) in his studies in the Santa Catalina Mountains of Arizona, and by Cooper ('I7) in a study of precipitation in redwood forests. The gauges used by Cooper had metal rather than glass containers, but were otherwise rather similar. The water was poured from the jar in which it collected into a graduate and this volume was converted into depth of precipitation by dividing the volume ofwater by the area of the mouth of the funnel. The period of observation included all the rains that fell within the year from August 28, I930, to August 28, I93I, and includes 48 periods of precipitation. Readings were made immediately after every rainfall. It may be well to mention briefly the salient features of the rainfall in *the Tucson region. There are two principal periods of precipitation, one usually occurring during the summer months from late June through July and August, and the other falling in the winter months during the period 3 3'

Cylindrocopturus Jatrophae Fall, a New Economic Insect

Serious damage to chrysanthemums in one garden in Tucson, Arizona, by a small stem borer proved to be due to a hitherto unrecorded insect pest. This was identified as Cylindrocopturus Jatrophae Fall, first discovered by Schwarz on Jatropha in the Santa Catalina Mountains. Jatropha is a native shrub of the family Euphorbiaceae.

On Bicycle and Afoot in the Santa Catalina Mountains

On Bicycle and Afoot in the Santa Catalina Mountains

Ecology of the Santa Catalina Mountains

Ecology of the Santa Catalina Mountains

Two New Species of Rusts

On a collecting trip at Takoma Park, Maryland, with Dr. G. G. Hedgcock, a caeoma-like species of Peridermium was collected on Pinus rigida Mill. which proved to be Peridermium delicatulum Arth. & Kern. Later, in looking over the species of Periderniuml in the Pathological Collections of the United States Department of Agriculture, hoping to find other collections of this rare species, the writer found a specimen on Pinus virginianla Mill., which from its gross characters appeared to be Peridernmiuml delicatulum, but a microscopic examination showed it to be an undescribed species. On a trip made during I9II through some of the forests of Arizona and new Mexico, the writer while descending the Santa Catalina Mountains found, on Coulrsetia glandulosa Gray, a rust which on microscopic examination proved to be an undescribed species intermediate in its generic position between Phragmopy.is Dietel and Calliospora Arth. Technical descriptions of these two fungi are given below.