This study examined the learning opportunities provided to students through the use of complex geological data supporting scientific inquiry. Through analysis of argumentative discourse in a high school Earth science classroom, uses of US Geological Survey (USGS) data were contrasted with uses of geoscience textbook data. To examine these differences, we conducted a review of frameworks for argumentation analysis, and through adaptation to the research foci of this study, developed a new analytic approach. Applying this approach to student classroom discourse revealed the affordances and constraints of both the complex USGS datasets and the filtered textbook data sources. The challenges of teaching with complex data are presented. (Contains 6 tables.)