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P. californica nymphs, or larvae, can grow to lengths in excess of 5 centimetres (2 in). The nymphs' dorsal side (back) is dark in color, although their ventral side (belly) is lighter. The coloring can vary, and subtle patterns are occasionally found on the abdomen.
P. californica is found across western North America, from British Columbia to California. They live in higher-velocity streams and rivers, on medium to large-sized unconsolidated substrates.