Tahoe event— A period of glaciation in the Sierra Nevada, occurring at the same time as the Perry Aiken glaciation in the White Mountains, approximately 18,000–140,000 years before the present. Questionably correlated with the midcontinental Illinoian glaciation.
talisman— Object believed to possess supernatural or magical properties.
talus— Accumulations of unstable rock fragments below steep slopes or cliffs.
taproot— A primary stout, vertical root that gives off small laterals but does not divide.
tarsus— The segment at the tip of the arthropod leg. (See Fig. 7.3.)
taxonomic rearrangement— An alternative classification scheme of a group of animals or plants.
tectonic— Pertaining to the rock structure and external forms resulting from the deformation of the Earth's crust.
tepals— Petal-like sepals, as in the buckwheats.
tephra— A collective term for all clastic materials ejected from a volcano and transported through the air, including volcanic dust, ash, cinders, lapilli, scoria, pumice, bombs, and blocks.
terete— Circular in cross section and more or less elongated; cylinder shape may be slightly tapering.
ternate— Arranged in threes.
terrigenous— Derived from the land or continent.
thorax— The section of the arthropod body to which the legs are attached. (See Fig. 7.3.)
threatened— As defined in the Endangered Species Act of 1973, refers to any species or subspecies likely to become endangered within the foreseeable future throughout all or a significant part of its range.
thrust (fault)— A reverse fault in which the inclination to the horizontal is 45° or less.
tibia— A leg segment between the femur and the tarsus. (See Fig. 7.3.)
Tioga event— The most recent glaciation of the Sierra Nevada, occurring the same time as the Middle Creek glaciation of the White Mountains, approximately 24,000–12,000 years before the present. Equivalent to the late Wisconsin glaciation of the midcontinent.
toposcale— Refers to phenomena that are closely related to topographic influences and are intermediate in size between mesoscale and microscale.
tor— A high, isolated crag, pinnacle, or rocky peak; commonly formed through periglacial processes.
torpor— Physiological dormancy in warm-blooded animals through lowered body temperature.
tourmaline— A complex group of silicate minerals; commonly associated in igneous rocks and occurring as three-, six-, or nine-sided prisms.
transcurrent fault— A large-scale, strike-slip fault (movement parallel to trend of fault).
tremolite— A monoclinic (i.e., crystal system characterized by either a single or twofold axis of symmetry) mineral of the amphibole group, Ca2 Mg5 Si8 O22 (OH)2 .
trend— The general term for the direction or bearing of a geological feature.
tribe— The division of a plant family. The large families are commonly divided into tribes.
tridentate— Having three teeth at the apex.
trilobite— An extinct marine arthropod belonging to the Class Trilobita, characterized by a three-lobed (head, middle body, and posterior, or tail) ovoid exoskeleton.
trimodal maximum— Having three nearly equal temporal peaks in the annual distribution of quantity, as for precipitation.
trough— A cyclonic (counterclockwise) bend in the horizontal airflow pattern in the synoptic (weather map) scale.
truncate— Squared at the tip or base as if cut off with a straight blade.
tumpline— Beltlike strap fitted to the head to aid in carrying heavy objects or to permit the free use of hands.
turbinate— Top-shaped, inversely conical.
turfy— Descriptive of a piece of soil bound by roots into a thick mat.