The Harkless Formation is mainly composed of
siltstones, with many layers of fine to medium-grained
quartzites, with
limestone within the lower parts of the formation, although differs in various parts of the formation. In the
Split Mountain area, the formation underlies the
Mule Spring Limestone, whilst in other areas it underlies the
Saline Valley Formation.
Members The formation contains two members, which are as follows, in ascending
stratigraphic order (lowest to highest): •
Weepah Member: Near the Andrews Mountain, at the type area of the formation, the member is dominated by greenish-gray and light-olive-gray siltstone, alongside a few layers of yellowish-gray fine to medium grained quartzite. The quartzite layers are identical to the layers found in the
Zabriskie Quartzite. The siltstone ranges from grayish-olive, pale-olive, and dark-greenish-gray, and is composed of silt-size grains within a matrix of
muscovite and
chlorite, and is thinly laminated. They have also slightly metamorphosed, resulting in
phyllite or
hornfels. The hornfels are primarily composed of muscovite, chlorite,
biotite, and
quartz. Trace fossils are relatively common within the type area. Within the
Esmeralda County, Nevada, the lower sections of the member is still dominated by siltstone, although this differs greatly from the siltstones higher up in the formation. This is due to the layers being quartzitic, coarser and more resistant to natural erosion. The sizes of the grains within these layers hovers around the boundary between coarse silt and very fine sand. •
Alkali Member: The upper Alkali member is composed of limestone layers, up to thick, inter-stratified with siltstone, and contain an abundance of
archeocyathid sponges. Further still there are light-brown limestone layers, only up to thick, that contain
Salterella, and are also inter-stratified with the siltstone layers in the middle of the formation. More limestone can be found at the top of the member, being gray or locally yellowish-brown, and up to thick. In some areas of the member, there are also tongues from the Zabriskie Quartzite, composed primarily of medium-grained quartzite, and can get up to thick in some places, and inter-stratify with the siltstones. The colour of the quartzite is commonly yellowish-gray or greenish-gray. It is also laminated to thin-bedded. Trace fossils are also common within these quartzite tongues, also appearing on the underlying siltstone layers. == Paleobiota ==