In this really great VIS image, taken by the NASA - Mars Odyssey Orbiter on June, 30th, 2002, and during its 2.404th orbit around the Red Planet, we can see a relatively small portion of the South/Western Flank of the Martian Volcano known as Hecates Tholus. The most interesting Scientific results - obtained by the European Space Agency's (or "ESA", for short) Mars Express Orbiter Mission - indicated (---> suggested) that a Major (---> Poweful, Huge) Eruption of Hecates Tholus took place - probably - about 350 Million Years ago. The Eruption created a Summit Caldera of about 10 Km (such as approx. 6,21 miles) in diameter. It has also been suggested that large Glacial Deposits - quite some time later - partly filled the Caldera itself, as well as an adjacent Depression.
The Impact Craters' Count of the area where Hecates Tholus stands, indicates that all these abovementioned events might have happened as "recently" as 5 to 20 Million Years ago. However, several Climate Models showed that the Ice is not stable at Hecates Tholus today, and such a circumstance points to a Major (and, most likely, Global) Climate Change that should have occurred when Hecates Tholus' Glaciers were still active. Furthermore, it has been suggested that the age of the Glaciers might correspond to a period of increased obliquity (due to still unknown reasons) of Mars' Rotational Axis.
Hecates Tholus' location is at approx. 32,12° North Latitude and 150,24° East Longitude, in the Martian Volcanic Province (or even "District") of Elysium, and it has a diameter of approx. 182 Km (such as about 113,022 miles); Hecates Tholus is the Northernmost of the Elysium Volcanoes (the others being, as you should know, Elysium Mons and Albor Tholus). Just out of curiosity, remember that in Planetary Nomenclature, a "Tholus" indicates a "Small Domical (---> Dome-shaped) Mountain" or "Hill"".
Latitude (centered): 31,0148° North
Longitude (centered): 149,2730° East
This image (which is an Original Mars Odyssey Orbiter false colors and Map-Projected frame published on the NASA - Planetary Photojournal with the ID n. PIA 18998) has been additionally processed, magnified to aid the visibility of the details, contrast enhanced and sharpened, Gamma corrected and then re-colorized in Absolute Natural Colors (such as the colors that a normal human eye would actually perceive if someone were onboard the NASA - Mars Odyssey Orbiter and then looked down, towards the Surface of Mars), by using an original technique created - and, in time, dramatically improved - by the Lunar Explorer Italia Team.