Conversation so far:
How did Michael Anthony's career start?
Michael Anthony continued his musical training by participating in marching band, while also pursuing athletics such as track and baseball
Where did Michael Anthony play in the marching band at?
In the mid-1960s Michael Anthony was relocated to Arcadia, California, where he continued his musical training by participating in marching band
What did Michael Anthony do after high school?
While attending Pasadena City College, Anthony met Eddie Van Halen who also took classes there and they would often see each other on campus. Bassist Mark Stone left Mammoth

Question: How was that band formed?
Self-contained rewrite: How was Mammoth formed after Mark Stone left Mammoth?