"my assignment for the so-called mushroom cult, earliest 1,000 b.c., is based on the excavations of kidder and shook at the verbena cemetery at kaminaljuyu. the mushroom stone found in this pre-classic grave, discovered in mound e-iii-3, has a circular groove on the cap. there are also a number of yet unpublished mushroom stone specimens in the guatemalan museum from highland guatemala where the pottery association would indicate that they are pre-classic. in each case the mushroom stone fragments has a circular groove on the top. mushroom stones found during the classic and post-classic periods do not have circular grooves. this was the basis on which i prepared the chart on mushroom stones which was then subsequently published by the wassons. based on carbon 14 dates and stratigraphy, some of these pre-classic finds can be dated as early as 1,000 b.c. the reference is in the following"...(see shook, e.m. & kidder, a.v., 1952. mound e-iii-3, kaminaljuyu, guatemala; contributions to american anthropology & history no. 53 from publ. 596, carnegie institution of washington, d.c. (letter from de borhegyi to dr. robert ravicz, mpm archives december 1st 1960 )