High-resolution mass spectrometry is currently used to determine the mass of biologically active compounds in plants and UHPLC-Orbitrap is a relatively new technology that allows fast fingerprinting and metabolomics analysis. In this work, several phenolic compounds including eleven phenolic acids, two fatty acids, two chromones and fourteen flavones were rapidly identified in the methanolic extracts of aerial parts and flowers of the unique Chilean species Ophryosporus triangularis Meyen, Asteraceae, growing in the Atacama Desert by means of ultrahigh resolution liquid chromatography orbitrap MS analysis (UHPLC-PDA-OT-MS) for the first time. The UHPLC-MS fingerprint generated can be used for the authentication of this endemic species. The methanolic extracts of the aerial parts and flowers showed also antioxidant capacities (65.34 ± 1.32 and 52.41 ± 1.87 μg/ml in the DPPH assay, 184.88 ± 13.22 and 196.80 ± 13.28 μmol TE/g dry weight in the ferric reducing power assay and 56.17 ± 3.03 and 65.41 ± 1.96% in the superoxide anion scavenging assay, respectively).