The province of Pavia, Lodi, Cremona and Mantua are in the Lombardy Region, in a chiefly plain but partly hilly area. The Lombard plains are part of the Po Valley. The name Po Valley (Italian: Pianura Padana o Val Padana) indicates a geographic region in northern Italy that coincides with the hydrographic basin of the river Po (in Latin "Padus", from which comes the Italian adjective "Padano"). It was the river Po, with its tributaries that formed the valley. The streams, coming down from the mountains, carried large amounts of debris along. The rivers dropped the debris on the bottom of the sea (5 million years ago the valley was actually a gulf of the Adriatic Sea) until in the end they filled it up.
The landfilling process, slow but unstoppable, lasted millions of years and still goes on today. The Po Valley borders the Alps on the North and West, the Apennines to the South and the Adriatic sea to the East. The Lombardy plain can be divided in two parts from the geological point of view: Upper and Lower Plains. The four provinces are located in the lower plains that are formed by clayey materials, little permeable and that slowly flows towards the Po. The passage from lower to upper plains, marked by natural resurfacing of water with such phenomena called resurgences or "fontanili" (springs) caused by the impact of the phreatic layer of upper plains with the non-permeable terrains of lower plains. These springs, thanks to their constant temperature ranging from 9 to 12° C have made it possible the use of a special type of crop farming called water meadows.