I finally read through the older biography by Taylor.
Here is Warren's account of July 1 (p 121-122): "I was away from Headquarters, and part of the time on the battlefield, on the 1st. When I left it, in the evening, I took a road east of the direct route to Taneytown, in order to increase my knowledge of the ground by seeing a new route. This road diverged very much from the direction I must take to reach Headquarters, and I was compelled to leave it, and take across country through woods and fields. By this I gained a good idea of the character of the country, but was late in reaching General Meade's camp. I found him about setting off for Gettysburg, and my report confirmed him in the determination he formed, on information sent by General Hancock, to concentrate his army at Gettysburg and fight there. The provisional line of Pipe Creek, which we had marked out some time previously, was not even thought of when the opportunity at Gettysburg presented itself.
I remained behind to rest and give orders and directions to my department, and so did not accompany General Meade. Next morning I set out for Gettysburg, and arrived there I cannot say what hour."