Face
The side of a cliff, escarpment, or other mostly vertical rock structure. The side of a geological structure, as in west facing slope.

Fault
A fracture or planar break in rock (which may be many miles long) along which there is movement of one side relative to the other.

Fauna
Animal assemblage in a geographic area.

FDA
Food and Drug Administration

Field Marks
Plumage or anatomical features of a bird that help to distinguish it from other similar species.

Fissure
An extensional crack, break, or fracture in the rocks.

Fissure Eruption
A volcanic eruption from a fissure or fracture in the earth. This type of eruption was common in southern Idaho. It usually results in basaltic lava spreading across wide areas without producing a large volcanic cone.

Flake
A thin piece of stone chipped away from a larger stone by striking it with another object.

Flash Flood
A local, sudden flood of water through a stream channel, generally of relatively great volume and short duration after intense local precipitation.

Floodplain
That portion of a river valley that is covered with water when the river overflows its banks.

Flora
Plant assemblage in a geographic area.

Fold
A curve or bend in rock strata, or layers.

Forbs
Weeds and herbs; low-growing annual or perennial plants.

Form
Shallow depression occupied by rabbits and hares.

Formation
A distinctive, mappable rock unit representing deposition under a uniform set of conditions and during a limited period of time.

Fossil
Any remains, trace, or imprint of a plant or animal that has been preserved in the Earth's crust since come past geologic or prehistoric time; loosely, any evidence of past life.

Fossorial
Adapted to digging or burrowing.

Freestanding Tent
Most dome tents and modified A-frame tents don't require staking to keep them standing (although the vestibules usually do). This makes for a tent that is easier to pitch, keep taut, and move around camp. You will want to stake it for maximum weather resistance.

Fremont Style
A rock art style ranging from western Utah to western Colorado. Believed to have been made between C.E. 400 and 1500. Anthropomorphs are usually square shouldered and roughly trapezoid in shape. These figures often overlap Barrier Canyon Style images.

Friable
Easily crumbled or pulverized.

FS
Forest Service.

Full-Grain Leather
In hiking boots, uppers using the full thickness of the cowhide. They tend to last longer and resist water better than split-grian leather.

Fumarole
A fumarole is a hole or vent from which gases rush into the air. A fumarole may be thought of as a hot spring which lacks liquid water.