title: Finding a branch point with Git?
body: <p>I have a repository with branches master and A and lots of merge activity between the two. How can I find the commit in my repository when branch A was created based on master?</p>
  
  <p>My repository basically looks like this:</p>
  
  <pre><code>-- X -- A -- B -- C -- D -- F  (master) 
            \     /   \     /
             \   /     \   /
               G -- H -- I -- J  (branch A)
  </code></pre>
  
  <p>I'm looking for revision A, which is not what <code>git merge-base (--all)</code> finds.</p>