This article examined the role of environmental interaction in interdisciplinary thinking and the use of different knowledge resource types. The case study was conducted with two classes (N = 40) of 8th-grade students, ages 13 to 14. The outdoor trail aimed to help students synthesize history, geography, and science knowledge. Two groups' discourse from each class was audio-­recorded and transcribed for content analysis. We coded the discourse to examine: (i) the use of different knowledge resource types (i.e., "contextual resource," "new conceptual resource," "prior knowledge resource"); (ii) the relationship among these knowledge resource types; and (iii) evidences of interdisciplinary thinking. Findings showed that contextual resources enhanced students' capacity to develop new conceptual resources and to activate prior knowledge resources. Further, about 80% of students' discourse demonstrated interdisciplinary connections of two subjects.