Significant environmental impacts such as climate change, reduction in biodiversity, increasing food scarcity, impacts on water supply and availability, and exacerbation of human health problems are occurring and are expected to increase. Despite these environmental challenges the teaching of California’s environmental literacy standards, the California Environmental Principles and Concepts (CA EP&Cs), in the K-12 public education system is infrequent and inadequate. The purpose of this study was to use a mixed methods approach to examine relationships between environmental identity (EI), personal environmental education teacher efficacy (PEETE), and peak stage of concern (SOC) for implementing CA EP&Cs for K-12 in-service teachers participating in regional 3-year California Environmental Literacy Projects (CELP). In the last year of CELP, a survey was given to 72 of the participating teachers to probe their EI, PEETE, and peak SOC for implementing CA EP&Cs. Eighteen months after the conclusion of CELP, five participating teachers engaged in a follow-up interview providing further insight about the relationships between EI, PEETE, and peak SOC for implementing CA EP&Cs. The findings from quantitative analysis of the survey and the qualitative analysis of the follow-up interviews indicate that participating teachers had high levels of EI and PEETE, and that there is a moderately large correlation between EI and PEETE within the sample of teachers surveyed. These high levels of EI and PEETE did not translate into impact level peak SOC in the Concerns-Based Adoption Model (CBAM) for most teachers. This finding demonstrates that environmental literacy professional development providers, site and district administrators, and teachers will have to overcome significant challenges to be able to increase the environmental literacy for students in California’s educational system. For environmental literacy professional development providers, it is suggested to surface teachers’ individual challenges to implementing CA EP&Cs and provide explicit recommendations to overcome these challenges. For district and site administrators, it is suggested that the CA EP&Cs be prioritized as important standards that are taught, and that student access to outdoor field experiences be valued and funded. For teachers, it is suggested to prioritize the teaching of CA EP&Cs and to integrate environmental literacy into the teaching of the various content areas where appropriate. Further details and additional suggestions are outlined in this research study.