The Ribiškės eroded hills are shaped like a large fan. This singular phenomenon was formed under very specific natural conditions. Years ago, the western part of the Vilnius City was covered by a glacier while the eastern part was a field of iced over moraine sediments. As the glaciers melted and retreated, the melting water accumulated in the plains of the Vilnia catchment basin. The water flowed to the west making irregular river beds and the currents were so strong that they erupted from underneath the present-time city territory creating unique relief shapes and labyrinths of dried out valleys. Compared to the ice, the water was warmer and thus it melted the soil which slid and creeped downwards rapidly deepening the already formed gullies. As Prof. Č. Kudaba likes to say, “Here, the sculptors of the earth’s surface gouged out hollows instead of molding the relief upwards”. Usually, hills rise high above the plains and plateaus. However, the Ribiškės hills seem to be sagged and sunken down into a gigantic hollow.
Ribiškės eroded hills are sometimes also called the eroded arroyo. This name is quite apt as the arroyo consists of an entire labyrinth of winding and intersecting gullies. It would be difficult to trace down the origins of water without a map. The hills here are the result of the erosion phenomenon, i.e. they are islands that remained not eroded by water.
The entire labyrinth of gullies and hills forms a regular fan shape in Ribiškės. A large arroyo (plain) stretches across its middle and is interspersed by smaller arroyos that seem to be branching out. The hills, arroyos and ridges seem to get more and more beautiful. Around 30 years ago, the entire hills could be seen clearly; however it got overgrown in forests. The Kaukysa Creek crosses the Ribiškės Hills in the middle. The name and origins of the creek lie in Baltic mythology. The mosaic of traditional farming lands and homesteads in the arroyos are also unique looking. Almost every homestead has its own artificial pond as apart from the Kaukysa Creek and smaller brooks, no other natural waterbodies are located nearby.