Microcracks were examined in five granite samples ranging in depth of origin from 696 to 1572 m by optical and scanning electron microscope observations and by elastic property measurements. The samples were obtained from the continuous crystalline core from Illinois deep borehole UPH 3 located in Stephenson County, Illinois. The core is a fine-grained granite at the top, and it becomes progressively coarser with depth. Cracks and fractures can be seen with the unaided eye in most of the core. Many of the larger fractures are coated or filled with secondary minerals. Long, narrow, tapered cracks which are open have not been observed in other midcontinent granites. These narrow cracks have sharp, matching edges and appear to be fresh. They are attributed to stress relief due to removal of the core by drilling. This interpretation is supported by measurements of velocity and strain as a function of confining pressure. The velocity and static bulk modulus at 1-bar pressure were smaller for samples originating from greater depths, indicating progressively greater stress relief cracking for deeper samples. The crack spectrum derived from the strain measurements showed that the majority of the crack porosity was for cracks with closure pressures between 150 and 225 bars. The conclusion that stress relief microcracks occur with greater concentrations in cores from greater depths implies that cautious interpretation must be made of laboratory measured physical properties which are sensitive to open microcracks.