The end-Permian mass extinction had a profound effect on shallow marine ecosystems and their biota. The effects of this event lasted for millions of years, and carbonate production did not fully recover until the Late Triassic. The Middle and Late Triassic periods corresponded to periods of development and expansion of both carbonate platforms and reef ecosystems. Our understanding of the evolution of shallow marine environments during the Triassic is based mainly on the study of the Tethyan systems. In contrast, the carbonate systems of the Panthalassa region are still largely unknown and have therefore contributed to the expansion of knowledge only to a limited extent. This difference is mainly due to the different state of preservation of outcrops and rocks in Tethys and Panthalassa. Unlike their Tethys counterparts, which were deposited mostly along passive margins, the carbonate systems of the Panthalassa region formed mainly in active tectonic environments, whose remains are now found, for example, as part of accretionary complexes and allochthonous landforms. Thus, during their depositional and post-depositional history, they underwent several tectonic events, which often affected both the quality of the outcrops and the preservation of the rocks, making their study difficult. The aim of this study is to deepen the knowledge of the Upper Triassic carbonate systems of the Panthalassa region. For this purpose, two study areas were selected: Northern California and Western Central nevada, USA. Both areas were subject to three field missions (four in total) in October 2018, June 2019, October 2019 and March 2022, during which the Upper Triassic carbonates of both areas were massively sampled, in order to include all relevant depositional environments. The samples were then analyzed using a combination of sedimentological, geochemical, and micropaleontological techniques. Great part of the samples were dissolved and processed for conodont extraction, allowing to recover more than 100 specimens.