The fertile Imotski Field is an interesting geological feature of the Geopark Biokovo-Imotski Lakes. Between the Imotski Field and Biokovo Mountain (1,762 m) there is a vast karstic area with rolling hills and valleys. The field and the karstic area in its immediate surroundings are rich water reservoirs. Stretching along the entire Imotski Field is the Vrljika River – a unique karstic sinking river which the locals call their "source of sustenance" because of the potable water springs which provide excellent agricultural conditions. The upper stretch of the Vrljika River was declared a protected  ichthyological reserve in 1971. When speaking about the geological diversity of the Geopark Biokovo-Imotski Lakes, it is important to highlight that this diversity of the southern coastal part is rather more pronounced in comparison to its northern interior part, and this is also one of the examples of the geological diversity of this entire area.  The hinterland of Geopark Biokovo-Imotski Lakes is thus a typical Dinaric high karst, a globally known locus typicus of specific karstic morphology. Its characteristic features are karstic fields (Imotski Field), lakes (protected Monuments of Nature and the globally important phenomena the Red and the Blue Lakes, the small lakes of Ričice, Galipovac, Knezovića and Mamića Lake, Proložac Lake – protected as a significant landscape in 1971, Lokvičićka lakes, Dva oka, etc.), rivers, canyons (Badnjevice canyon), hills, springs (Krčevac and Opačac springs), sinkholes, caves (Zovnjača cave) and pits. Furthermore, as we move southward, closer to the coastal part of the Geopark Biokovo-Imotski Lakes, we come across the magnificent Biokovo Mountain which has the status of a nature park. Biokovo Mountain is part of the Dinaric mountain range and as such stretches in a northwest – southeast direction. The Eocene flysch bedrock makes up most of the lower parts of the mountain, on the south side as well as the north face, while the higher elevations are formed from Mesozoic carbon-rich sediments. The base of the central part of Biokovo is a gently sloping plateau rising cca 300 meters above sea level, and it is fertile and green due to its flysch layers. Extending out from this "green belt" is the most impressive part of the rock, rising up to 1,000 meters in height and acting as a screen which separates the coast from the hinterland. Stretched out along the tops of these rocks is a 3-4 km wide undulating plateau with abundant karstic features and a gentle and gradual slope towards the hinterland. Dolines (sinkholes) are the dominant features of this mountain. Some are very deep, even more than 100 meters. Some are collapsed, while some extend into deep pits. This specific shape of surface karst landforms is called polygonal or moonlike karst because it resembles craters on the surface of the Moon. All typical karst phenomena are also featured on Biokovo – dolines, karrens, tinajitas (small depressions), caves (Krjava, Baba, Jujnovića cave and many other), ice caves and pits (Njemica – the deepest pit in Biokovo, 863 meters). The Mokre noge pit (-831 m) and the Amfora pit (-788 m) are some of the more important pits of Biokovo.