Knott's Berry Farm's Facebook Page said:Link
Today the left rear wheel detached from one of Knott’s Berry Farm’s stagecoaches with 14 passengers on board, causing the coach to tip to its side. Three guests were transported to a local hospital for minor injuries; two have been released as of 5:00pm. The ride will be closed until further notice. Guest safety is Knott’s number one priority.
Also in a post from a guest that was at the park that day was a picture... not the best of quality but it's from the GP so what more can you expect...
The the link to the picture can be found here