Description: The foothill yellow-legged frog has a grey, brown, or reddish dorsum, or the back of the frog. It is commonly spotted or mottled, but occasionally is plainly colored. Adults have yellow coloration under their legs, which may extend to their abdomens, but this characteristic is faint or absent in young frogs.

A triangular, buff-colored patch occurs on the snout, and, unlike other frogs in the genus, there is no eye stripe. The throat and chest are often boldly mottled; and the species has indistinct dorsolateral skin folds and granular skin. Males of this species develop nuptial pads on their thumb bases during the breeding season. These frogs can be identified by their rough skin, horizontal pupils, fully webbed hind feet, and their habit of jumping into moving water.

Tadpoles of this species, though, resemble those of the western toad, Bufo boreas. R. boylii as tadpoles have fairly flattened tails that lack color at the end and are the tallest in the midsection. The mouths of the tadpoles are made for suction to rocks, with labial teeth rows used for scraping algae and diatoms, unicellular algae with cells walls that contain silica, off of the rocks to which they are clinging. The mouth of the young R. boylii is also helpful in identifying it from B. boreas because the young foothill yellow-legged frogs develop more defined teeth rows after three weeks, while their counterparts do not.

Both the Columbia spotted frog and the Cascades frog, also part of the genus Rana, live in the northern regions of this frog's territory.

Habitat: Foothill yellow-legged frogs are highly aquatic and almost always found in, or within a short distance from, water. The most frequently used habitats are streams, springs, and freshwater lakes, with a preference for rocky-bottomed creeks; it usually occurs in gently flowing water. Slow-flowing creeks or streams with cobble-sized pebbles are preferred egg laying sites for foothill yellow-legged frogs. Adults often spend the majority of their time sitting on rocks in the stream or nearby on the banks. If startled, however, they will immediately leap into the water and swim swiftly to the bottom. In clear waters, they will take cover under overhanging rocks; in streams with muddy bottoms, they will stir up the silt and hide in the mud. They may occur at any elevation from sea level up to 7000 feet.

Range: Foothill yellow-legged frogs occur in the Coast Ranges from the Santiam River in Marion County, Oregon south to the San Gabriel River in Los Angeles County and along the west slopes of the Sierra/Cascade mountain ranges in most of central and northern California. Other isolated populations have been reported in the Baja California Norte, in southern California, and at Sutter Buttes in Butte County, California. The species is found at elevations ranging from sea level to 6,700 feet in Baja California Norte. In California, foothill yellow-legged frog have been recorded in the Sierra as high as 6,000 feet near McKesick Peak, Plumas National Forest and 6,365 feet at Snow Mountain at the boundary of Lake and Colusa Counties.

Found in these States: CA | OR

Diet: Food supplies, such as algae the tadpoles eat, also affect the sexual maturity of the species. Reportedly, the "amount of protein in different algae, can affect size at and time to metamorphosis" and "these food effects may be mediated through diet-induced changes in thyroid function", which means the food the tadpoles ingest dictates the changes in the thyroid gland's production of certain proteins. Tadpoles most commonly feed on algae, diatoms, and detritus. As the species grows older, it changes its diet to animal tissue which must be swallowed whole because the frog's jaw is structured on a hinge joint that does not allow for sideways movement as in humans. Adult frogs eat a range of foods such as moths, ants, grasshoppers, hornets, beetles, flies, water striders, and snails.

Reproduction: The mating "ceremonies" begin in spring, when adult frogs congregate on sandy and/or rocky bars to mate. Previously believed to mate from March to May, recent experiments have shown the time to be closer to April to late June. High stream velocities, however, may dislodge R. boylii egg masses from oviposition substrates. Thus, R. boylii avoids rapid waters to protect the egg masses from being swept away. This technique is why the species has a long breeding season. If the conditions do not meet their standards, they refuse to mate and wait until the water velocities go back down to ideal.

For the foothill yellow-legged frog, oviposition, or the depositing of eggs, is somewhat sporadic because delays such as rains could cause problems such as unwanted removal of eggs. The males also perform mating calls mostly underwater, and those above the water are faint and hard to hear over 165 feet. After the frogs have successfully mated, the egg masses are laid attached to rocks underwater in streams and rivers with flow velocities ranging from 0.1 to 0.6 m3/second.

These egg masses can contain 100 to 1000 eggs in one batch, contained in a bluish gel that disappears once the eggs take on water, and the dark ovum, the center of egg, is covered by three jelly envelopes about 0.2 inches in diameter. Eggs hatch in about five to over thirty days depending on the temperature that the mass is at and the surrounding water. The tadpoles continue to stay associated with the egg mass for several days, and continue to need higher temperatures to grow quickly. By the time the tadpoles reach about 40 mm, roughly 1.5 inches, they are adults and their reproductive organs are mostly functional. The frogs are usually fully developed by the summer after their first metamorphosis, though some begin breeding after six months.

Status: Along with the problems associated with pesticides being washed into this frog's habitat, in Trinity County, California, a dam on the major river of the frog's home has affected about 94% of the possible procreation areas for the frogs, which has endangered the population.

Subspecies: None

Taxonomy: