Along with Yathong and Round Hill Nature Reserves, Nombinnie forms part of one of the largest contiguous blocks of Mallee in western NSW. The majority of the reserve is located on the extensive dune fields of the Darling depression. Some areas of riverine plains are present near Willandra Creek.

Apart from the mallee, the vegetation is made up of stands of white cypress pine woodlands, woodlands of bimble box and red box, black box in depressions, lignum, belah woodlands in association with western rosewood, wilga, leafless cherry and warrior bush.

A variety of endangered fauna including malleefowl, red lored whistler, southern scrub robin and pink cockatoo are present in the reserve. Over 90 species of birds are known from the area.

Principal management objectives include the maintenance of habitat diversity, encouragement of regeneration and protection of rare plant and animal species. Research and educational activities are encouraged where compatible with nature conservation objectives.