The Iryagi ['irjagi] is the second longest mountain range of Ilethes, running for over 5,000km down Marcasia, first southwestwards from Misia then turning southeast at Erdia, dividing the continent two-thirds northwest and one-third southeast. The range is as narrow as 18km at its northern end, but as wide as 420km towards the continental interior. The range's northern continuation on Istheusia is known as the Taza-a Lami, and its southern extension on Arophania the Alerryagi. The three ranges are collectively known in geology as the Western Boundary Mountain System.
The name Iryagi derives from the Arithide word ryagi, "mountain range", from ryāg, "mountain", and simply means "the I mountain range". There is still debate over the origin of the toponym "I", especially over whether it bears any relation to the identical autonym of the Areth.
The Iryagi were formed through crustal uplifting as the convergent Marcasian and Maellorian plates collided. The denser oceanic Maellorian slid under the lighter continental Marcasian, but, due to an unusually small difference in density between the two at the plate boundary (the western edge of the Maellorian has its own landmass), the subduction was particularly frictive, leading to much folding of the crust and sedimentation that gave rise to the mainly metamorphic rock of the range today. The great tension generated from the awkward and unwieldy collision was to provide the underlying cause for many disastrous future volcanic eruptions and earthquakes.
The range is of a generally uniform climate of the temperate sort, with temperatures averaging 20°C and precipitation around 60mm, and serves as the border between the more temperate south and the warmer northern parts of the continent. Due to this congenial climate, the range is heavily forested, and vegetation is primarily of the deciduous type. Snow lines are typically absent in the north of the range, but may reach as low as 2,400m near Erdia.