a gall, similar to the one made by P. proxima, is made by a species on the native S. lasiandra in the Sierra Nevada and adjacent ranges at elevations of 1660-2200 m, and it is unlikely that it will prove to be P. proxima.

[A photo of these galls appears in Figure 5A, page 6 of the pdf]

Pontania proxima [Russo makes no distinction between Pontania proxima and the species mentioned by Smith. They are assumed to be distinct because Smith speculates this is the case and because no US native willows, including Salix lasiandra, are listed as hosts of Euura proxima by Liston et al 2017]
Bean-gall sawfly
[Page 223]

Hosts: Salix lasiandra (S. lucida subsp. lasiandra)

Galls protrude equally on both sides of host leaves and are smooth, glabrous, and red on top and yellow-green underneath.