Westward the Dream (Ribbons West #1) by Judith Pella and Tracie Peterson

As the U.S. descends into the Civil War, photographer Brenton Baldwin travels west with his sister Jordana, taking pictures of the developing lands and in search of their sister. Along for the trip is young Caitlan O'Connor, who has just arrived from Ireland. Will they make it to California to find their family despite the danger that looms ahead? And can early romance grow into love in the face of trials and tragedy?