Wrinkle ridges are features created by compressive tectonic forces within the maria. These features represent buckling of the surface and form long ridges across parts of the maria. Some of these ridges may outline buried craters or other features beneath the maria. A prime example of such an outlined feature is the crater Letronne. A wrinkle ridge is a type of feature commonly found on lunar maria. These features are low, sinuous ridges formed on the mare surface that can extend for up to several hundred kilometers. Wrinkle ridges are tectonic features created when the basaltic lava first cooled and contracted. They frequently outline ring structures buried within the mare, follow circular patterns outlining the mare, or intersect protruding peaks. They are sometimes called veins due to their resemblance to the veins that protrude from beneath the skin. These are found near craters. Wrinkle ridges are named with the Latin designation dorsum (plural dorsa). The standard IAU nomenclature uses the names of people to identify wrinkle ridges on the Moon. Thus the Dorsa Burnet are named for Thomas Burnet, and the Dorsum Owen is named after George Owen of Henllys. Wrinkle ridges can also be found on Mars, for example in Chryse Planitia, as well as on several of the asteroids that have been visited by spacecraft, as well as Mercury, and a couple of moons of Jupiter and Saturn. Letronne is the lava-flooded remnant of a lunar crater. The northern part of the rim is completely missing, and opens into the Oceanus Procellarum, forming a bay along the southwestern shore. The formation is located to the northwest of the large crater Gassendi.To the west-southwest is the flooded crater Billy, and north-northwest lies the smaller Flamsteed. The surviving rim of Letronne is now little more than a semi-circular series of ridges. The flooded, broken rim of Winthrop overlies the western wall. The rim is the most intact along the eastern stretch, forming a mountainous promontory into the mare. A small cluster of central rises lie at the midpoint of the crater. A wrinkle ridge traverses the floor from north to south, and outline a portion of the missing rim. The crater floor is otherwise nearly smooth and relatively free of craterlets, with the exception of Letronne B near the southeast rim.A ridge is a geological feature consisting of a chain of mountains or hills that form a continuous elevated crest for some distance. Ridges are usually termed hills or mountains as well, depending on size. There are several main types of ridges: Dendritic ridge: In typical dissected plateau terrain, the stream drainage valleys will leave intervening ridges. These are by far the most common ridges. These ridges usually represent slightly more erosion resistant rock, but not always – they often remain because there were more joints where the valleys formed, or other chance occurrences. This type of ridge is generally somewhat random in orientation, often changing direction frequently, often with knobs at intervals on the ridge top. Stratigraphic ridge: In places such as the Ridge-and-valley Appalachians, long, even, straight ridges are formed because they are the uneroded remaining edges of the more resistant strata that were folded laterally. Similar ridges have formed in places such as the Black Hills, where the ridges form concentric circles around the igneous core. Sometimes these ridges are called "hogback ridges". Oceanic spreading ridge: In tectonic spreading zones around the world, such as at the Mid-Atlantic Ridge, the volcanic activity forming new plate boundary forms volcanic ridges at the spreading zone. Isostatic settling and erosion gradually reduce the elevations moving away from the zone.