The Hon Yen island complex belongs to Nhan Hoi village, An Hoa commune, Tuy An district, located 15km from Tuy Hoa city along the coastal road, including two small islands, Hon Sun near the shore and Hon Yen outside, these islands both originate from Dai Nga basalt formation. At Hon Yen, there is columnar basalt, the composition is dense basalt, tholeit basalt, the columns are tilted towards the sea, unlike Da Dia reef in Tuy An district, the basalt columns here are not cut into discs but form long columns. The basalt columns are mainly 5-sided and 6-sided, less often there are 4-sided and 3-sided types; the average diameter of the column cross-section is 35cm. On the mainland, Mui Yen reveals dark gray basalt, dense basalt composition, strongly cracked. Hon Sun consists of tuff volcanic debris, tuff sand, and basalt fragments.

Geological characteristics of the heritage and Outstanding value of geological heritage.

Aesthetics: The unique structure and morphology of columnar basalt and the types of basalt that make it up, together with the surrounding natural landscape, create aesthetic inspiration not only for scientific research but also for the creation of various art forms (painting, photography, sculpture, etc.).
Geological heritage types: type B (geomorphology), type D (rock).