Northern Prairie Wildlife Research Center
Wingspan 4.0 cm. Forewing is strongly falcate, pale yellow to orange, with narrow basal and median lines. This geometrid is widely distributed in wet conifer forests of western North America. Moths fly in fall. Caterpillars are generalist feeders on the foliage of flowering trees and shrubs, such as maple (Acer), alder (Alnus), chinquapin (Chrysolepis chrysophylla), snowberry (Ceanothus velutinus), salal (Gaultheria shallon), ocean spray (Holodiscus discolor), azalea (Rhododendron), elderberry (Sambucus), and snowberry (Symphoricarpos albus).
Similar species: Synaxis fuscata is smaller and paler in color, occurs in pine forests and juniper woodlands east of the Cascades, moths fly in fall; Synaxis pallulata has broad black basal and median lines, is widely distributed, flies in fall, and the caterpillars feed on the foliage of species of Pinaceae.