The Forest Trail at the Riežupe estuary to the Venta crosses the nature park “Riežupe”. It is created to protect the impressive natural values characteristic of Riežupe valley: its slopes and ravine forests and its geological natural monuments, such as sandstone outcrops, caves, waterfalls, river streams, as well as species, forest massifs and landscape. Riežupe caves are artificially excavated in the sandstone layers of the Amata suite. These layers were formed in the Devonian period about 365 million years ago, when the present territory of Latvia was located near the equator and was covered by a shallow sea. Iron oxides, clay particles and sand cemented, forming a sediment known as sandstone. Its colour (yellow, red, white) and hardness depend on the iron content and the degree of cementation. Plant and animal fossils are often found in sandstone layers. Fossils of the most primitive quadruped, Ventastega curonica, which lived 365 million years ago, have been found on the banks of the Ciecere river. Self-extraction of fossils by damaging sandstone outcrops is not allowed!