Aunt Jane's Nieces And Uncle John by L. Frank Baum

Aunt Jane's Nieces and Uncle John picks up the continuing story of the three cousins Patsy Doyle, Beth De Graf, and Louise Merrick, and their family; the plot of the book begins three days after the wedding of Louise and her fiancé Arthur Weldon, the event that concluded the sixth book in the series, Aunt Jane's Nieces in Society. Uncle John hires a touring car and the party makes a tour of the South West, visiting New Mexico and Arizona. (Summary by Lynne Thompson)