I encountered this score by Joseph Byrd this morning.
http://renewablemusic.blogspot.com/2008/08/joseph-byrd-fish-1961.htmlwhich makes one wonder how many other pieces of this type existed before Terry Riley's
In C. (Apparently this was published in La Monte Young's
Anthology: but my copy only has the instructions, not the dots).
The early history of American minimalism usually credits only four composers: I suspect the true number should be much higher.
Let's hear it for Terry Jennings, for example.
And here's a some info about Dennis Johnson by Kyle Gann.
http://www.artsjournal.com/postclassic/2007/10/remembering_november.html