For July 8, I can show two postmarks, one on an UX7, and the other is a postcard, but a rather odd card. In fact, I have another card (Jul 22) that is quite similar, both seem to be advertisements for the described offering.
The UX7 is one man's registration in California's Great Register. Mailed from Ukiah to the county clerk in Humboldt County, it records that Charles March was 27 years old, a native of Ohio, and worked as a laborer in Little River, Mendocino County.
The other Jul 8 card was mailed aboard the Eureka & Scotia RPO from Fortuna. The author of the card apologized for using the card, an offer from The New Home Sewing Machine company.
I'll show that Jul 22 card as well. Sent from Northspur was this ad for a copy of the "Girl in Red". This was apparently included with a new pair of shoes?