The larger felsic dike, about 10 meters thick, is composed of monzonite that cuts through the middle of the plug and extends through the notch and over the top of the Butte. The notch has formed because the monzonite weathers more quickly than the alkali-gabbro. Augite is the main mafic mineral. The smaller mafic dike, visible only from the east side, is an alkali-lamprophyre. Lamprophyres are a complex group of dark alkaline igneous rocks that share mineralogical similarities with some kimberlites.
Dark minerals occur as phenocrysts and in the lamprophyre groundmass.
Top Figure 2 Thin-section of monzonite porphyry from central dike of Huerfano Butte Photo courtesy of Dr. Brian Penn Remote Sensing Remote sensing reveals through photos and images the stocks, dikes, plugs, and other intrusive features that dominate the landscape of the study area. A satellite image, unlike a photograph, is a rendition of a target's features depicted through the use of spectral reflectance and stored digitally. These reflectance values are stored in a form suitable for input into a computer. Software and hardware designed to analyze these images provides the ability to see a pictorial representation of remotely sensed targets. Landsat 5 images, taken at an altitude of 705 kilometers, provides a synoptic view of the Spanish Peaks area.