The Municipality of San Mariano (now Maragusan) was created on November 25, 1977 by virtue of Presidential Decree 1247 separating it from Mabini, its mother municipality.  A far off and secluded valley of Compostela Valley, the municipality is surrounded by rolling hills and mountainous terrain, which serve as its natural shield against strong winds.  Its elevation ranges from 2,000-7,642 feet above sea level.  In the past, the land was solely inhabited by Mansakas, the local tribal aborigines who used to live in the mountains where they eked out a meager living through the primitive “kaingin” system of agriculture.  They   identified   themselves   as   those   from “Man-Agusan”, a native word meaning settlers along Agusan River.  This is so because Agusan   River, whose sources are within the valley’s boundaries, meanders through several barangays of the municipality.  For phonetical reason, the local word, “Man-Agusan” was changed to MARAGUSAN thus; the encompassing gentle plains of Maragusan, Caragan and Tag-ugpo came to be known as MARAGUSAN VALLEY.

 The area was accidentally discovered by air by Captain Rivera, a pilot and a rancher at Lake Leonard, Masara, Maco, Davao while traveling off course in 1955.  He plotted the area with the Bureau of Lands and verified it as a potential agricultural land.   He then applied for a thousand hectares agricultural farm in the heart of the valley.

 While the papers were in process, Capt. Rivera opened a settlement in the nearby Agwacan Spring with Albino Segura as the head of the group and in-charge of the development of the settlement.  Capt. Rivera supplied the planting materials, such as coffee and cacao seedlings.  But he was not able to set foot on Maragusan soil since the 1,000-hectare agricultural land was not granted to him by the Bureau of Lands due to some restrictions.

 Albino Segura then resigned as the foreman of the settlement and worked on a farm of his own.  He worked for the release of the portion of the valley as agricultural land.  He then invited more settlers from everywhere to farm the unoccupied areas of the rich valley, while Arsenio T. Yanong, Sr. took the position as the new foreman of the settlement of Capt. Rivera.

 Pacio Acas, a Mansaka, was then the tribal head of the valley.  It was in 1956 that Segura, a Boholano, was appointed as sub-teniente del barrio of the valley and served for a few succeeding years.  Then in 1962, the valley was created a regular barrio of Mabini and named Maragusan.  Mr. Agripino Bariarcal was the first elected Barrio Lieutenant and the first Barangay Captain after the law was enacted renaming Barrio Lieutenant to Barangay Captain.

 The remote and isolated municipality had no direct route to its mother town. A heavily forested zone cut off the valley from vital government services, thereby giving lawless elements/dissidents free reign over the area.  This situation prompted the then District Councilor Manolo T. Yanong to spearhead the petition way back in 1972 for the creation of Maragusan Valley into a separate municipality named San Mariano.  The seat of the government was located at the townsite of Maragusan containing an area of 92.2 hectares.

 Florentino R. Obeso was the first mayor (appointed) and was installed January 24, 1978.  In the 1980 local elections, the then District Councilor Manolo T. Yanong was elected and became the first elected Municipal Mayor.

 In 1986, as a result of the EDSA Revolution, a revolutionary government was established installing new sets of national and local officials.  Vice Mayor Jose D. Perez, Sr. was then appointed OIC Mayor.  The new set of officials submitted a position paper requesting Her Excellency President Corazon C. Aquino to change the name San Mariano into its original name.  Finally, through a House bill authored by Hon. Lorenzo S. Sarmiento, Sr., the then Congressman, First District, Davao Province, Republic Act 6678 was approved on October 12, 1988 changing San Mariano to its original name MARAGUSAN. 

With the enactment of Republic Act 7160 or the Local Government Code of 1991, Manolo T. Yanong was re-elected mayor in 1992 synchronized national-local elections and served the municipality until 1998. Various projects had been established under his initiatives that brought the municipality in the limelight of tourism destinations in the region.  In was also during the latter’s term where a multi-national company – Stanfilco Dole Philippines established its banana farm in the municipality producing the exportable cavendish variety. He was succeeded by Gerome S. Lamparas, Sr. serving the municipality for one term only, 1998-2001. It was during his term where the municipal government had a reorganization which remarkably streamlined the remuneration disparity between department head and next in rank. Gerome S. Lamparas, Sr. did not participate the 2001 local elections. He was succeeded by Arsenio L. Yanong, Jr. who served the municipality for two terms, from 2001 to 2007.

 Being young and dynamic who started to serve as mayor at the age of 35, Arsenio L. Yanong, Jr. advocated innovations in governance especially in adopting new technologies and strategies to intensify public service. Bringing the government services closer to the people through “Barangayan”, Computerizations and the likes were initiated.  It was during his term where Maragusan was opened to the world when Smart Communications Company established its wireless telecommunication services in Maragusan. Similarly, Globe Telecommunications opened its services that widened up the information-communication opportunities for Maragusan. With meager public resources to pursue development programs, the municipality was able to establish and strengthen its linkages with partner NGOs and private sectors for resource mobilization. Kasilak Development Foundation, Incorporated in collaboration with Catholic Relief Services and Stanfilco – Dole Philippines supported the construction of the Maragusan Livelihood and Enterprise Development Center (MLEDC) and Maragusan Agro-Enterprise Trading Center (MAETC), the construction of Bangay Pinoy water system project, the Maragusan Valley Area Resource Development Project, and the Formulation of Land Use Based Barangay Development Plans of all barangays. Paglilingkod Batas Pangkapatiran Foundation on the other hand assisted the Mansaka tribe in the formulation of the Ancestral Domain Sustainable Development and Protection Plan (ADSDPP) while Agri-Aqua Development Coalition-Mindanao assisted the municipal government in strengthening people’s organization in the grassroots.

 As the home of the Mansaka-Mandaya tribes and in pursuance of RA 8371 otherwise known as the Indigenous Peoples Rights Act, the Karagan Valley was included in the issuance of the Mandaya Tribe Certificate of Ancestral Domain Title on February 17, 2004. It has a coverage area of 4,464.1442 hectares.

 The continuing aspiration for progress and development of the municipality was always coupled with challenges and obstacles. It was on August 5, 2006 when the municipal public market in barangay Poblacion was wiped out by fire causing displacements to more than a hundred families owning business establishments and residential buildings.

 The 2007 local elections has changed the leadership and administration of the municipality. Cesar C. Colina, Sr. was elected mayor and is serving the municipality to present. With the desire to be of great service to his constituents, he introduced reforms in governance as espoused by his exposure on corporate management. Seeing the necessity of basic infrastructure to pump prime rural development, he immediately pushed for the construction of farm to market roads linking sitios to barangays; initiated disaster risk reduction program through mitigation projects like construction of drainage and flood control; and introduced improvements in the aesthetics of government buildings and landscapes. Similarly, the new public market was constructed maximizing local funds only. In 2008, the new public cemetery was opened and operated for public use.  In 2009, he started the construction of the new transport terminal. As the man of action, he instigated paradigm shift in governance making municipal government processes more responsive and efficient to public needs and demands.