Echinocereus pacificus grows solitary, in clumps of 30–60 cm (12–24 in) in diameter containing around 100 stems.

Stems are cylindrical to elongated shoots 5 to 6 cm (2.0 to 2.4 in) long, with 10 to 12 ribs and a 4 to 5, strong, upright central spine that is white or light gray with a darker tip, measuring 25 mm (0.98 in) in length.

Additionally, there are 10 to 12 spreading, straight, whitish or grayish radial spines that are 5 to 10 mm (0.20 to 0.39 in) long.

[2] Chromosome count is 4n=44[3] There are two recognized subspecies:[4] Plants are found growing on granite slopes and xeric scrub in Baja California, Mexico at elevations around 110 to 2600 meters.

Plants are found growing along with Adenostoma fasciculatum, Stipa speciosa, Arctostaphylos peninsularis, Dudleya pulverulenta, Lotus rigidus, Nolina microcarpa, Pinus monophylla, Rhamnus crocea, Opuntia phaeacantha, Cylindropuntia acanthocarpa, Pinus quadrifolia, Ferocactus viridescens and Malosma laurina.