Ceanothus velutinus with blister galls on the undersides of leaves, along the Green Creek trail, east of Green Lake, Mono County, CA. Galls appear to be from Eriophyes ceanothi, a parasitic Eriophyid mite specific to Ceanothus.
References:
https://www.cdfa.ca.gov/plant/ppd/PDF/Bulletin1939_EriophyidStudiesV.pdf
https://naldc.nal.usda.gov/download/CAT87208955/PDF