Circular to arcuate features, observed on winter Landsat Multi-Spectral Scanner images of flat lying Paleozoic, karsted sedimentary rocks of the northwestern portion of the Rolla 1� x 2� quadrangle of Missouri, appear to be related to Precambrian basement structures. These features were best displayed using a selective band composite using the visible green and two infrared bands. The perimeters of the rings correspond to anomalous gravity and magnetic highs, while petrographic analysis of samples from basement cores showed that these anomalies correlate well with mafic rocks (e.g. diorite, gabbro). This suggests that high-level mafic intrusions (e.g. ring dikes, laccoliths) may be present in the otherwise dominantly felsic Precambrian of Missouri. Ring fractures in collapsed calderas are known to exist in the easternmost part of the state where the Precambrian surface lies close to or at the surface. Remotely sensed circular features there are commonly attributed to stream valleys which follow the old caldera margins, basement topographic highs, and more rarely, cryptoexplosive structures.

Although the basement in the study area is covered by more than 1500 feet of sedimentary rock, the observed features also correlate well with some surficial stream valleys, reminiscent of those valleys following the caldera margins in areas of less cover. In addition, they correlate well with an elongated low on a structure contour map of the top of the Cambrian, and show a slight correspondence to surface sinkhole concentrations. While the genetic relationship between the Precambrian anomalies and surface expression could not be positively identified, one possible interpretation is that arcuate fractures may have propagated up into the overlying Paleozoic carbonate section, thus localizing development of sinkholes, which upon collapse, form the observed features.