Combining Mark Edwards' (Markal) 'Eskalon' .ter terrain with some other elements has produced what appear to be the remnants of a volcanic cone and lava flows surrounded by a fertile landscape. The dirt and spring is high in sulphur; hence the title and yellowish tint in the soil.
Thanks to Matt for the mackerel sky cloud formation file; Walli for the dry shrubs (available at NWDA) and klas for the grass. Also, thanks to John Robertson (Schmeerlap) for the procedure on building up surface layers.