About Chris officially joining, Mick says: "Before we went on the road in America with that album [Kiln House], we asked her to join."
Chris: "Ten days later I was in America, in New Orleans. I'd never been to America in my life... with Fleetwood Mac! I couldn't believe it."
Mick: "She learned the songs in New Orleans before the first show."
On Wikipedia it says Kiln House was recorded during June and July 1970 and was released September 18. The last show before the recording was May 28 in London, with an additional show on July 9. The first show after the recording of Kiln House was on August 1 at the Warehouse Cafe in New Orleans. Judging by what Christine and Mick say on the Mick Fleetwood Story dvd, I imagine Chris joined sometime at the end of July 1970, with her first show on August 1.
Just for kicks, here are some pictures from August 28-29 (or a few days before/after) 1970 in NYC, shortly after Christine went on tour.
Also, does anyone have an exact date for the day Jeremy left the band? I'm watching The Mick Fleetwood Story and Mick says he left around the time of the earthquake in LA. I did a little bit of research into February 1971 earthquakes in California. One happened on February 9, at 6:0o am, in the San Fernando Valley. Then Mick says, "that afternoon, maybe within three hours, he was gone." So, does February 9 sound correct? (I'm aware that Jeremy might not have announced his departure
that day, considering he was 'missing' for anywhere between three to five days. So, I guess it could've happened somewhere between the 12-15th after the band found him.)
From Wikipedia: "Shortly before a journey of the band from San Francisco to Los Angeles, LA experienced a major earthquake. Being in a fragile mental state and filled with strong negative premonitions, Spencer was very apprehensive about having to travel to LA. He unsuccessfully pleaded with Fleetwood to cancel this leg of the tour. Shortly after arriving in LA, and on the day of a gig the group was scheduled to perform at the Whiskey A Go Go, Spencer left the hotel room he shared with Fleetwood to visit a bookshop on Hollywood Boulevard. Spencer did not return, however, forcing the cancellation of that evening's concert, while the band and members of their entourage went searching for him. Some days later, he was found to have joined the religious group the Children of God, and he declared that he no longer wanted to be involved with Fleetwood Mac."
However, according to the Fleetwood Mac Legacy tour dates page, FM had dates scheduled for Feb. 11, 12, 13, 14 at the Fillmore West in San Francisco. There was another gig on the 19th in San Bernardino, and after that they went to the east coast. It says Jeremy's last concert was on February 14.