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Debra L. Block

Publications and source records attributed to Debra L. Block.

12 recordsLinked to original sources
USGS2018

The Colorado River and its deposits downstream from Grand Canyon in Arizona, California, and Nevada

Understanding the evolution of the Colorado River system has direct implications for (1) the processes and timing of continental-scale river system integration, (2) the formation of iconic landscapes like those in and around Grand Canyon, and (3) the availability of groundwater resources. Spatial patterns in the position and type of Colorado River deposits, only discernible through geologic mapping, can be used to test models related to Colorado River evolution. This is particularly true downstream from Grand Canyon where ancestral Colorado River deposits are well-exposed. We are principally interested in (1) regional patterns in the minimum and maximum elevation of each depositional unit, which are affected by depositional mechanism and postdepositional deformation; and (2) the volume of each unit, which reflects regional changes in erosion, transport efficiency, and accommodation space. The volume of Colorado River deposits below Grand Canyon has implications for groundwater resources, as the primary regional aquifer there is composed of those deposits. To this end, we are presently mapping Colorado River deposits and compiling and updating older mapping. This preliminary data release shows the current status of our mapping and compilation efforts. We plan to update it at regular intervals in conjunction with ongoing mapping.

Arizona, California, Nevada↗
USGS2017

Geologic map of the northern White Hills, Mohave County, Arizona

Introduction The northern White Hills map area lies within the Kingman Uplift, a regional structural high in which Tertiary rocks lie directly on Proterozoic rocks as a result of Cretaceous orogenic uplift and erosional stripping of Paleozoic and Mesozoic strata. The Miocene Salt Spring Fault forms the major structural boundary in the map area. This low-angle normal fault separates a footwall (lower plate) of Proterozoic gneisses on the east and south from a hanging wall (upper plate) of faulted middle Miocene volcanic and sedimentary rocks and their Proterozoic substrate. The fault is part of the South Virgin–White Hills Detachment Fault, which records significant tectonic extension that decreases from north to south. Along most of its trace, the Salt Spring Fault dips gently westward, but it also has north-dipping segments along salients. A dissected, domelike landscape on the eroded footwall, which contains antiformal salients and synformal reentrants, extends through the map area from Salt Spring Bay southward to the Golden Rule Peak area. The “Lost Basin Range” represents an upthrown block of the footwall, raised on the steeper Lost Basin Range Fault. The Salt Spring Fault, as well as the normal faults that segment its hanging wall, deform rocks that are about 16 to 10 Ma, and younger deposits overlie the faults. Rhyodacitic welded tuff about 15 Ma underlies a succession of geochemically intermediate to progressively more mafic lavas (including alkali basalt) that range from about 14.7 to 8 Ma, interfingered with sedimentary rocks and breccias in the western part of the map area. Upper Miocene strata record further filling of the extension-formed continental basins. Basins that are still present in the modern landscape reflect the youngest stages of extensional-basin formation, expressed as the downfaulted Detrital Valley and Hualapai Wash basins in the western and eastern parts of the map area, respectively, as well as the north-centrally located, northward-sagged Temple Basin. Pliocene fluvial and piedmont alluvial fan deposits record postextensional basin incision, refilling, and reincision driven by the inception and evolution of the westward-flowing Colorado River, centered north of the map area.

Arizona↗
USGS2014

Geologic map of the eastern quarter of the Flagstaff 30’ x 60’ quadrangle, Coconino County, northern Arizona

The eastern quarter of the Flagstaff 30′ x 60′ quadrangle includes eight USGS 1:24,000-scale quadrangles in Coconino County, northern Arizona (fig. 1, map sheet): Anderson Canyon, Babbitt Wash, Canyon Diablo, Grand Falls, Grand Falls SE, Grand Falls SW, Grand Falls NE, and Meteor Crater. The map is bounded by lat 35° to 35°30′ N. and long 111° to 111°15′ W. and is on the southern part of the Colorado Plateaus geologic province (herein Colorado Plateau). Elevations range from 4,320 ft (1,317 m) at the Little Colorado River in the northwest corner of the map area to about 6,832 ft (2,082 m) at the southwest corner of the map. This geologic map provides an updated geologic framework for the eastern quarter of the Flagstaff 30′ x 60′ quadrangle and is adjacent to two other recent geologic maps, the Cameron and Winslow 30′ x 60′ quadrangles (Billingsley and others, 2007, 2013). This geologic map is the product of a cooperative effort between the U.S. Geological Survey (USGS) and the Navajo Nation. It provides geologic information for resource management officials of the U.S. Forest Service, the Arizona Game and Fish Department, and the Navajo Nation Reservation (herein the Navajo Nation). Funding for the map was provided by the USGS geologic mapping program, Reston, Virginia. Field work on the Navajo Nation was conducted under a permit from the Navajo Nation Minerals Department. Any persons wishing to conduct geologic investigations on the Navajo Nation must first apply for, and receive, a permit from the Navajo Nation Minerals Department, P.O. Box 1910, Window Rock, Arizona 86515, telephone (928) 871-6587.

Arizona↗
USGS2014

Historical channel-planform change of the Little Colorado River near Winslow, Arizona

This study evaluates channel-planform adjustment on an alluvial reach of the Little Colorado River and documents the geomorphic evolution of the channel through an analysis of aerial photographs and orthophotographs for the period 1936–2010. The Little Colorado River has adjusted to the effects of an extreme flood in 1923 and a subsequent decline in peak discharge and mean annual flow by channel narrowing: the channel width and area of the river have decreased by approximately 90 percent over the study period. Although deposition historically exceeds erosion, lateral migration exacerbates localized erosion, particularly near hydraulic controls. Despite repeated cutoff and avulsion, the Little Colorado River has steadily increased in length and sinuosity over a period of 74 years. Changes in temperature and precipitation are likely affecting the discharge of the Little Colorado River near and downstream of Winslow, Ariz. Nonparametric methods of trend detection determine whether the probability distribution of temperature, precipitation, and peak streamflow has changed over time. Time-series plots of temperature and precipitation show statistically significant trends at the 99-percent-confidence level when evaluated with a Mann-Kendall test. An increasing trend was indicated in mean daily minimum air temperature (T min ), whereas decreasing trends were indicated in both annual precipitation (P ann ) and monsoon-seasonal precipitation (P jas ), as well as in peak discharge.

Arizona↗
USGS2014

Digital database of microfossil localities in Alameda and Contra Costa Counties, California

The eastern San Francisco Bay region (Contra Costa and Alameda Counties, California) is a geologically complex area divided by faults into a suite of tectonic blocks. Each block contains a unique stratigraphic sequence of Tertiary sediments that in most blocks unconformably overlie Mesozoic sediments. Age and environmental interpretations based on analysis of microfossil assemblages are key factors in interpreting geologic history, structure, and correlation of each block. Much of this data, however, is distributed in unpublished internal reports and memos, and is generally unavailable to the geologic community. In this report the U.S. Geological Survey microfossil data from the Tertiary sediments of Alameda and Contra Costa counties are analyzed and presented in a digital database, which provides a user-friendly summary of the micropaleontologic data, locality information, and biostratigraphic and ecologic interpretations.

California↗
USGS2013

Geologic map of the Winslow 30’ × 60’ quadrangle, Coconino and Navajo Counties, northern Arizona

The Winslow 30’ × 60’ quadrangle encompasses approximately 5,018 km 2 (1,960 mi 2 ) within Coconino and Navajo Counties of northern Arizona. It is characterized by gently dipping Paleozoic and Mesozoic strata that dip 1° to 2° northeastward in the southwestern part of the quadrangle and become nearly flat-lying in the northeastern part of the quadrangle. In the northeastern part, a shallow Cenozoic erosional basin developed about 20 million years ago, which subsequently was filled with flat-lying Miocene and Pliocene lacustrine sediments of the Bidahochi Formation, as well as associated volcanic rocks of the Hopi Buttes Volcanic Field. The lacustrine sediments and volcanic rocks unconformably overlie Triassic, Jurassic, and Cretaceous strata. Beginning about early Pliocene time, the Little Colorado River and its tributaries began to remove large volumes of Paleozoic and Mesozoic bedrock from the map area. This erosional development has continued through Pleistocene and Holocene time. Fluvial sediments accumulated episodically throughout this erosional cycle, as indicated by isolated Pliocene(?) and Pleistocene Little Colorado River terrace-gravel deposits on Tucker Mesa and Toltec Divide west of Winslow and younger terrace-gravel deposits along the margins of the Little Colorado River Valley. These gravel deposits suggest that the ancestral Little Colorado River and its valley has eroded and migrated northeastward toward its present location and largely parallels the strike of the Chinle Formation. Today, the Little Colorado River meanders within a 5-km (3-mi) wide valley between Winslow and Leupp, where soft strata of the Chinle Formation is mostly covered by an unknown thickness of Holocene flood-plain deposits. In modern times, the Little Colorado River channel has changed its position as much as a 1.5 km (1 mi) during flood events, but for much of the year the channel is a dry river bed. Surficial alluvial and eolian deposits cover extensive parts of the bedrock outcrops over the entire Winslow quadrangle.

Arizona↗
USGS2011

A dryland river transformed—the Little Colorado, 1936–2010

The Little Colorado River, in northeastern Arizona, is a major tributary of the Colorado River. Over a span of 74 years, the U.S. Geological Survey (USGS) has mapped substantial migration of the river channel between the City of Winslow and the Navajo Nation community of Leupp (Tólchíí kooh). In a human lifetime, the river has moved more than 1 mile across its valley floor. Channel migration and flooding pose a considerable risk to the life and property of people living near the river. USGS scientists are working to better understand the potential for further channel adjustments and flooding to help provide communities at risk with the information they need to address these threats and make future development decisions.

Arizona↗
USGS2006

Geologic map of the Peach Springs 30' x 60' quadrangle, Mohave and Coconino counties, northwestern Arizona

This map is a product of a cooperative project of the U.S. Geological Survey, the U.S. National Park Service, and the Bureau of Land Management to provide geologic map coverage and regional geologic information for visitor services and resource management of Grand Canyon National Park, Lake Mead National Recreation Area, Grand Canyon-Parashant-National Monument, and adjacent lands in northwestern Arizona. This map is a synthesis of previous and new geologic mapping that encompasses the Peach Springs 30' x 60' quadrangle, Arizona. The geologic data will support future geologic, biologic, hydrologic, and other science resource studies of this area conducted by the National Park Service, the Hualapai Indian Tribe, the Bureau of Land Management, the State of Arizona, and private organizations. The Colorado River and its tributaries have dissected the southwestern Colorado Plateau into what is now the southwestern part of Grand Canyon. The erosion of Grand Canyon has exposed about 426 m (1,400 ft) of Proterozoic crystalline metamorphic rocks and granite, about 1,450 m (4,760 ft) of Paleozoic strata, and about 300 m (1,000 ft) of Tertiary sedimentary rocks. Outcrops of Proterozoic crystalline rocks are exposed at the bottom of Grand Canyon at Granite Park from Colorado River Mile 207 to 209, at Mile 212, and in the Lower Granite Gorge from Colorado River Mile 216 to 262, and along the Grand Wash Cliffs in the southwest corner of the map area.

Arizona↗
USGS2004

Geologic map of the Lower Grand Wash cliffs and vicinity, Mohave County, Northwestern Arizona

This digital map database is compiled from unpublished data and new mapping by the authors and represents the general distribution of surficial and bedrock geology in the mapped area. Together with the accompanying pamphlet, it provides current information on the geologic structure and stratigraphy of the area. The database dilineates map units that are identified by age and lithology following the stratigraphic nomenclature of the U.S. Geological Survey. The scale of the source maps limits the spatial resolution of the database to 1:31,680 or smaller.

Miscellaneous Field Studies Map↗
USGS2003

Geologic map of the Hiller Mountain Quadrangle, Clark County, Nevada, and Mohave County, Arizona

Map Scale: 1 :24,000 Map Type: colored geologic map The Hiller Mountains Quadrangle straddles Virgin Canyon in the eastern part of Lake Mead. Proterozoic gneisses and granitoid rocks underlie much of the quadrangle . They are overlain by upper Miocene basin-filling deposits of arkosic conglomerate, basalt, and the overlying Hualapai Limestone. Inception of the Colorado River followed deposition of the Hualapai Limestone and caused incision of the older rocks. Fluvial gravel deposits indicate various courses of the early river across passes through highlands of the Gold Butte- Hiller Mountains-White Hills structural block . Faults and tilted rocks in the quadrangle record tectonic extension that climaxed in middle Miocene time.

Report↗
USGS2002

Surficial Geologic Map of The Loop and Druid Arch Quadrangles, Canyonlands National Park, Utah

This geologic map is a product of a cooperative project between the U.S. Geological Survey and the U.S. National Park Service to provide geologic information about this part of Canyonlands National Park, Utah. This digital map database contains bedrock data from previously published data that has been modified by the author. New mapping of the surficial deposits represents the general distribution of surficial deposits of the Druid Arch and The Loop 7.5-minute quadrangles.

Miscellaneous Field Studies Map↗