Data from process monitoring, geophysical surveys, and postburn core studies were integrated to delineate the extent of affected coal and overburden at the Hanna IV A and B underground coal gasification experiment sites in southeastern Wyoming. The experiments were conducted from December 1977 to September 1979 in the Hanna No. 1 coal bed of the Eocene Hanna Formation. A postburn coring and well logging program was initiated in the fall of 1983. Well locations were selected using cavity boundary predictions determined by process monitor wells, a high-resolution seismic survey (June 1983). Detailed coal and overburden core studies were completed, including petrographic and scanning electron microscopy, X-ray analyses, strength tests, maceral analyses, vitrinite reflectance, fluorescence analyses, and proximate analyses. The Hanna IV A and B experiments apparently produced two distinct, temperature-stratified cavities separated by a fault zone of minor total displacement. Maximum coal consumption occurred near the west end of the IV A pattern, producing an asymmetrical cavity. Overburden collapse reached 45 ft. (14 m) above the top of the coal seam. Zones of maximum roof collapse are commonly bounded by minor faults that act as planes of weakness along which overburden fails. Override was a significant problem at the IV B pattern, primarily caused by faulting. A high percentage of calcite cement and sufficient porosity in the overburden contributed to limited roof collapse away from the faults. High-temperature mineral assemblages and fluorescence spectral parameters indicate that burn temperatures exceeded 2191/sup 0/F (1200/sup 0/C). The zone of reaction apparently is narrow (approx.6 in. (0.15 m)). 41 refs., 28 figs., 6 tabs.