Andrena are small to medium-sized, often metallic bees, recognizable by their elongate abdomens, facial foveae in females, hairy-faced males, and banded abdomen tips.

Small (6 mm), burly, non-metallic bees with black head/thorax, pale-striped or red abdomens, a sharply ridged smooth-to-pitted thorax, and—unlike Megachile—an arolium pad between tarsal claws.

Diadasia bituberculata specializes on bindweed and morning glory flowers, with long mouthparts and females bearing long, widely-spaced pollen hairs on their hind legs.

Bombus melanopygus is a stout, mid-sized bumble bee with pale yellow hair and black wing-base bands; northern populations show red-orange abdominal segments, black at Mount Diablo.

Bombus californicus is a mostly black, mid-to-large bumble bee with yellow hair in front of the wings, a black band between wing bases, and an always-yellow 4th abdominal tergum.

Anthophora californica is black with non-hairy ivory bands on each abdominal segment; females have green eyes and hind-leg scopae, males have spiny red hind tibiae.

Brachymelecta californica is a cuckoo bee of Anthophora nests, with broken white hair stripes on the abdomen, gray-white thorax/head hair, and (formerly Xeromelecta) females lacking leg scopae.

Perdita californica is a small (6 mm), colorful bee with a gold/red abdomen, two submarginal cells, and a large wing stigma.

Habropoda depressa is a stout gray bee with brownish appressed abdominal hair, white outer hind-leg scopae, a broad flat head, and a first recurrent vein reaching near the second submarginal cell's apex (vs. Anthophora).

Perdita interrupta is a tiny (4-5 mm), metallic blue bee with incomplete ivory abdominal bands, an ivory-white face, and a short, abruptly-ending wing cell.

Trachusa perdita is a black, pale-striped bee with grayish hair; males have a white clypeus, and females show a pollen scopa under the abdomen.

Anthidiellum notatum robertsonii is a compact yellow-and-black bee with an overlapping head shelf and extended scutellum over the propodeum, unlike Dianthidium.

Chelostoma californicum is a medium (8-9 mm), cylindrical black bee with white abdominal hair bands, an elongated scutellum, and scissor-like mandibles in females.

Colletes are medium, fuzzy bees with a triangular hairy face, a hair-striped tapered abdomen, long hind-leg scopae, and an S-shaped second recurrent vein.

Stelis are cuckoo bees, mostly metallic black to blue-green, lightly haired with incomplete pale markings, no leg scopae, and 2 spines on the middle tibia.

Dianthidium are yellow-and-black, mostly hairless bees with 2 submarginal cells, paper-thin pronotal lobes, and yellow running along the inner eye margins.

Anthophora edwardsii has a mostly dark abdomen without bold hair bands. There can be a metallic bluish sheen to abdomen.

Melecta edwardsii is a medium-large bee with cream-haired thorax, a blue-black hairless abdomen, black under-wing hairs, and distinctive long scutellar spines.

Eucera (subgenus Synhalonia) males have long black antennae and tan clypeus hair; females have a dark clypeus, squared abdomen, and broad, flat-topped head.

Xylocopa tabaniformis orpifex is the smallest local carpenter bee (12-18 mm); females are metallic black with smoky wings, males tan-faced with tan thorax hair.

Mount Diablo's Hoplitis bees are sleek, elongate, black or metallic green, with abdominal pollen scopa and an arolium pad on front tarsal claws (unlike Megachile).

Hylaeus are tiny (3-8 mm), slender, wasp-like black bees with yellow face and leg markings, little hair, and no female scopae; males show more facial yellow.

Lasioglossum are variable, often shiny bees (2-8 mm) with an arched basal wing vein, 2-3 submarginal cells, and hair bands at segment bases (unlike Halictus).

Melecta separata callura is a medium-large (~15 mm) cuckoo bee of Anthophora nests, black with white patching on abdomen and legs, and females lacking scopae.

Megachile are mostly medium, black or gray, whitish-striped bees, often hairy with facial bumps; females have abdominal scopae, males blunt abdomen tips.

Melissodes are medium-large bees (13-15 mm) with males' long, bicolored antennae, medial abdominal hair bands, plumose scopae (vs. Eucera), and a large marginal cell.

Nomada are wasp-like cuckoo bees of Andrena nests, nearly hairless, red/yellow/black, 2-12 mm (usually medium), with females lacking leg scopae.

Osmia are compact, metallic bees (blue, purple, green, or black), with abdominal pollen scopa and a front-leg arolium pad, unlike Megachile.

Anthophora pacifica females are all dark with white hind scopae and a bluish abdomen; males have white mid-tarsal fringes, white terga 1-2, and yellow facial patches.

These small (5-8 mm) early-season, community-nesting bees are mostly hairless and black, with a yellow clypeus, a truncated wing marginal cell, and 2 submarginal cells.

Protosmia rubifloris is a small-medium black bee (~7.5 mm) with white abdominal hair bands; females have slender forward mandibles and a spatula-like clypeal process.

The Red-tailed Micro-Shortface Bee is a tiny (4-6 mm) Rophitinae sweat bee with low-set antennae, orange-red terga 1-3, a dark head, and 2 submarginal wing cells.

Ceratina are small, metallic gunmetal green/black carpenter bees, nearly hairless, females with a yellow clypeal mark, males a white anchor-shaped facial patch.

Halictus tripartitus is a small (5-6 mm) bee with a dull green metallic thorax, apical abdominal hair bands, an arched basal wing vein, and a broad, toothless head.

Anthophora urbana has white bands at the tergal segment tips, well-developed hind-leg scopae, and bluish eyes.

Xylocopa sonorina is a very large bee (18-26 mm) with an inflated abdomen; females are dark and shiny with purplish-coppery wings, males blonde-haired with green eyes.

Bombus vosnesenskii is a stout, large, mostly black bumble bee with yellow hair in front of the wing bases and on its square face and head top.