My guess for the date of this photo is based entirely on the sleeves. In 1932, Gilbert Adrian created a gown with exaggerated ruffled sleeves for the film Letty Lyndon. It created a fashion sensation. Not only were there exact copies for sale, but all kinds of puffed, billowed, and fluttering sleeves became a fashion feature that lasted for years.
It took time for the new trend in sleeves to make it to the mass market. The 1933 Sears catalogs have some examples of inventive sleeves, but by 1934 they flooded the pages.
The younger woman on the left in my photo wears sleeves similar to the dress on the left in the 1934 Sears offering. Her older companion (perhaps her mother?) wears much longer sleeves that might be open to her forearm or cuffed like some of the dresses on the Sears page. The small prints, and especially the polka dots, are another indication that the photo comes from the Depression decade.
Where are they off to? The mountain highway could be just about anywhere, including here in Southern California. They look look quite dressed up with their hats. Was there perhaps a special event at the end of the journey?