sr 77/oracle road multimodal corridor profile study final report - Pima ...

4. PHYSICAL AND NATURAL ENVIRONMENT
This chapter identifies the pertinent environmental characteristics of the SR 77 Corridor. It also
provides a basis for an environmental screening of the corridor to identify environmental
constraints.
4.1 GENERAL TOPOGRAPHY, VEGETATION, AND CHARACTER OF THE
CORRIDOR
The SR 77 Corridor is part of the Basin and Range physiographic province, one of the three
geological provinces in Arizona. Basin and Range topography is characterized by mountain
ranges that trend northeast-southwest, separated by deeply in-filled valleys. The SR 77 Corridor
passes through a valley flanked by the Tortolita Mountains to the west and the Santa Catalina
Mountains to the east; both are classified as metamorphic core complex ranges. The SR 77
Corridor gradually, but steadily, increases in elevation from approximately 2,300 feet at the
southern terminus (Tucson) to approximately 4,200 feet (Oracle), and vegetation in the corridor
changes along this elevational gradient. The southernmost portion of the corridor is surrounded
by the City of Tucson. The corridor crosses the Rillito River within the city limits. Continuing
north, the corridor passes through areas of native vegetation typical of the Arizona Upland
Subdivision of the Sonoran Desert. This biotic community is characterized by saguaro, palo
verde, mesquite, brittlebush, and various other cacti and annual species. The Towns of Oro
Valley and Catalina also are located within this biotic community. At the junction of SR 77 and
SR 79, the vegetation shifts to semi-desert grassland, with an increase in the abundance of
mesquite. Other common plants of this biotic community include soaptree yucca and various
grass species. As the corridor approaches Oracle, oak and pinyon pine trees become part of the
vegetation composition. Exhibit 4-1 shows a list of the common plants along the SR 77
Corridor.
Invasive, non-native plants are common along the SR 77 Corridor. The most pervasive species
include buffelgrass, fountain grass, and Lehmann’s lovegrass. These grasses can have many
ecological ramifications, including competition with native species, change in species
composition, and change in fire disturbance regime. These species are all hardy perennial
bunchgrasses that fill the areas between widely-spaced native species, creating fuel for fire.
These species are fire-adapted, which means that after a fire, they can dominate the landscape
and exclude native Sonoran Desert species, which are not fire-adapted. This is of concern in
transportation projects because vehicle traffic increases human-caused fire potential.
4.2 WILDLIFE
The habitats in the corridor support numerous smaller mammals, birds, and reptiles. Exhibit 4-2
lists common fauna associated with each biotic community.
4.3 SPECIAL STATUS SPECIES AND HABITATS
In the state of Arizona, there are 52 species of plants and animals that are listed as threatened or
endangered by the U. S. Fish and Wildlife Service (USFWS). These species and their habitats
SR 77/Oracle Road Multimodal Corridor Profile Study May 2007
Final Report Page 4-1