Mount Pleasant Caldera rock. The Intercaldera Sequence comprises formations that crop out from overlying flows in triangularly shaped area, and includes thick volcanic ash (tuff), thick breccia layers, and intermediate to felsic igneous rocks that tend to intrude the above layers and are typically located along caldera margin faults. The Exocaldera Sequence contains ash flow tuffs, mafic lavas, alluvial redbeds, and porphyritic felsic lavas that are distributed across five different layers. The late Caldera-Fill Sequence contains rocks that are similar to those of the outflows of the other, older layers, and comprises two formations and two relatively minor intrusive lava flows. The volcanic
Grayson Glades Natural Area Preserve Grayson Glades Natural Area Preserve Grayson Glades Natural Area Preserve is a Natural Area Preserve located in Grayson County, Virginia. Its centerpiece is an extremely rare wetland type known as a "mafic fen", which are situated upon soils rich in magnesium and fed by springs. The site is at the headwaters of a small stream system supporting additional mafic fens. Among the rare species found on the property are tuberous grass-pink ("Calopogon tuberosus"), ten-angled pipewort ("Eriocaulon decangulare" var. "decangulare"), large-leaved grass-of-parnassus ("Parnassia grandifolia"), queen-of-the-prairie ("Filipendula rubra"), sticky false-asphodel ("Triantha glutinosa") and Canada burnet ("Sanguisorba canadensis"). The preserve is owned and