In Lawvere's article Comments on the Development of Topos Theory, the author writes:
Similarly, Grothendieck and others unerringly recognized which kinds of mathematical structures are 'preserved by all functors which preserve finite limits and arbitrary colimits'. (A very impressive list was produced by Grothendieck  during his 1973 stay in Buffalo; during the same visit he advocated the abandonment of his earlier complicated definition of 'scheme', but unfortunately the simpler alternative he offered does not seem to have found its way into the textbooks.)
The reference in the bibliography reads:
 A. Grothendieck, List of classes of structures, 1973 (now in J. Duskin's file.)
Can anyone direct me to a copy of this document? I haven't been able to find one.