Throughout the southwestern United States, vegetation in what historically was grassland has changed to a mixture of trees and shrubs; exotic grass species and undesirable shrubs have also invaded the grasslands at the expense of native grasses. The availability and amount of soil nutrients influence the relative success of plants, but few studies have examined fire effects on soil characteristics in a temporal, spatial, and species group-specific fashion. Likewise, few studies have tied fire effects and ecological aspects to the underlying geology. Our research investigates the effects of fire events on selected soil characteristics pH, nitrate (NO3-), plant-available phosphorus (PO4-3), and total organic carbon (TOC) on native grass-, exotic grass-, and mixed grass-dominated plots distributed on four different geological surfaces. Treated and control plots were sampled prior to burn treatment and at intervals after the burns. In addition to new geologic mapping of the study areas, results indicate the geologic substrate is the most important variable for explaining pH, NO3- and PO4-3 values in the soils. Dominant grass type – native, non-native, or mixed – had little effect on the response of soil geochemistry to fire events: post-burn results indicate vegetation was a significant factor only for TOC. Recovery to pre-burn levels varies with characteristic: there were no significant initial differences between vegetation types, but significant differences in NO3-, PO4-3, and TOC amounts occur as a result of fire events, geological characteristics, and time. The research helps identify the soil response to fire and the recovery times of soil characteristics, further defines which fire frequency is optimal as a management strategy to maximize soil macronutrient contents, and illustrates the important role geology plays in grassland ecosystems.

In 2006, Arizona enacted legislation that directed the Arizona Geological Survey (AZGS) to map earth fissures in the state, required that the presence of earth fissures be disclosed in real estate transactions, and that the resultant earth fissure maps be made publicly available. In order to meet these statutory requirements, AZGS developed, for the first time, standards, procedures, and criteria for identifying, mapping, and characterizing earth fissures.

AZGS geologists identified earth fissures through a review of publications and reports, air photo analysis, and field reconnaissance. Using GPS, we collected relatively high-precision locations and descriptive data along the length of earth fissure surface exposures, and categorized them as either continuous or discontinuous. If we were not able to find and map previously reported fissures, we used the “reported, unconfirmed” category.

A series of small earth movements occurred along the slopes of State Route 87 at about mile marker 224 (between the Bush Highway and Route 188) throughout the winter of 2007‐2008, culminating with a landslide on Friday, 21 March 2008. This landslide buckled the southbound lanes, displaced the northbound lanes, and closed the highway for nearly a week. The mass movements occurred on slopes that were constructed with re‐vegetated, laid back slopes; soil nail walls; and rip rap‐lined channels. However, our reconnaissance mapping indicates that most, if not all, of the slope movements are located within a much larger, older landslide adjacent to, and cut by, SR‐87. No specific trigger for the landslides was immediately apparent, although a combination of factors (e.g., precipitation, groundwater levels, etc.) may have contributed to conditions for the slope failure. Headscarps of various types of landslides are present along both sides of the highway. Results from our preliminary investigation indicate that up to three other paleo‐landslides may be present in the immediate vicinity. The full extent and nature of these landslides are unknown and require further investigation to evaluate their potential to be reactivated and risk they pose to the highway.

This field trip guide was created for a Project WET conference held in Tucson, Arizona, June, 2007. This guide discusses the general geology of the Santa Catalina Mountains in Sabino Canyon, and points out evidence of the July 2006 floods and debris flows. There are stops in the first few miles of canyon, and towards the end of the tram road, where the most spectacular debris flows are located.

In order to begin to assess debris‐flow hazards along the Santa Catalina Mountains in Pima County, we mapped the extent and character of relatively young prehistoric debris‐flow deposits in detail at fifteen
canyon mouths. Mapping was conducted on a scale of 1:6,000 using aerial photographs, detailed
topography, and field relationships. Deposits were classified into relative age categories based on
topographic relationships, soil development and surface characteristics of the deposits. Ages of selected
debris‐flow deposits in four canyons – Soldier, Sabino, Finger Rock and Pima – were estimated using
radiocarbon (14C) and cosmogenic (10Be) isotope methods.

Evidence of past debris flows were found in all fifteen canyons. Relative age dating, corroborated by
10Be, indicates the largest and most extensive deposits in all canyons are late Pleistocene to early
Holocene in age. Events from 2006 show that some potential exists for debris flows to exit the mountain front into developed areas near canyon mouths.

The goal of this study is to develop a method for identifying potential post-fire debris flow hazard areas prior to the occurrence of wildfires, providing more time for local governments and emergency planners to develop and execute hazard mitigation strategies. This pilot study focuses on the communities of Pine and Strawberry, which are located in forested canyons at the base of the Mogollon Rim in north-central Arizona. Results from this project will provide local agencies, emergency planners and land managers more effective tools for prioritizing watershed treatment areas and implementing mitigation measures to alleviate potential impacts and threats from post-fire debris flows to infrastructure, human life, and property in a timely and cost-effective manner.