Soon after, Harrison left for
Pasadena, California, for his residency at the
California Institute of Technology (Caltech), while Kitty remained in Philadelphia to complete her bachelor's degree in botany at the University of Pennsylvania, and was then offered a postgraduate research fellowship at the
University of California, Los Angeles. At Caltech, she worked with physicist
Charles Lauritsen: the
X-ray laboratory at Caltech used for physics research was also used for experimental cancer therapy research. It was at a garden party thrown by Lauritsen and his wife Sigrid in August 1939 that she met
Robert Oppenheimer, a physicist who taught at Caltech for part of each year and the remaining time at
University of California, Berkeley. Soon after, they began an affair, one which they did not even attempt to conceal: they were frequently seen around town in Robert's car. At Christmas time she went to
Berkeley without her husband, to spend time with Oppenheimer. Oppenheimer invited Harrison and Kitty to spend the summer at his New Mexico ranch,
Perro Caliente. Harrison declined, as he was engaged in his research, but Kitty accepted.
Robert Serber and his wife
Charlotte collected Kitty in Pasadena, and drove her to
Perro Caliente, where they met up with Robert, his brother
Frank Oppenheimer, and his wife Jackie. The Serbers had met Kitty before, at Charlotte Serber's parents' house in Philadelphia in 1938. The Serbers loved to ride through the pine and
aspen forests and floral meadows of the
Sangre de Cristo Mountains, camping with minimal food and equipment. Kitty impressed them with her riding ability; horsemanship was a normal accomplishment for women of her social class, and she had learned to ride as a girl on the riding trails around Aspinwall. Kitty and Robert rode out to stay the night with his friend Katy Page in
Los Pinos, New Mexico. The following day Page rode to
Perro Caliente on her
bay horse to return Kitty's nightgown, which had been left under Robert's pillow. Kitty later told Anne Wilson that she got Robert to marry her the "old-fashioned way"—by getting pregnant. In September 1940, Robert informed Harrison, and they agreed that the best way forward was for Kitty to get a divorce so she could marry Robert. Soon after, Robert shared a podium with Nelson to raise money for refugees from the Spanish Civil War, and he informed him that he was engaged to Kitty. Nelson's wife was also pregnant, and he named his daughter, who was born in November 1940, Josie in memory of Dallet. To obtain a divorce, Kitty moved to
Reno, Nevada, where she stayed for six weeks to meet the state's residency requirements. The divorce was finalized on November 1, 1940, and Kitty married Oppenheimer the following day in a civil ceremony in
Virginia City, Nevada, with the court janitor and clerk as witnesses. ==Manhattan Project==