Numerous types of soils on the Earth's surface are formed by the weathering of parent rock materials under the influence of various factors, resulting in soils having various layers. In the field of pedology, soil layers are referred to as soil horizons, which are divided into two terms: genetic horizons and diagnostic horizons. This study focuses on observing diagnostic horizons at endopedon. Understanding the development of horizons plays a role in assisting the naming of soils in the Soil Taxonomy classification developed by the USDA. South Kalimantan is part of a wet tropical climate region, with some of its soil parent materials being the result of the weathering of ultrabasic rocks. The aim of this research is to further identify the development of the endopedon horizon in soil formation from ultrabasic rocks in different slope positions, with the purpose of providing information on the development of ultrabasic rocks in West Mandiangin Village, Banjar Regency, South Kalimantan. The establishment of the Oxic horizon in Profile-1 is found at a depth of 20 cm to 68 cm from the soil surface. The conformity of the Oxic horizon in Profile-2 is located at a depth of 35 cm from the soil surface. The development of the Oxic horizon is a result of latosolization processes, and this is related to the basic nature of the soil-forming materials, allowing the latosolization process to proceed well, supported by environmental conditions such as climate and rainfall in the research location.