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The earliest stages of protostellar evolution are notoriously difficult to characterize observationally due to their dense extincting envelopes and the necessity for long wavelength observations, but recent surveys have made great strides in this area. We have assembled a complete sample of 40 Class 0 and 90 Class I sources (with envelope masses > 0.1 Msun) in the Perseus, Serpens, and Ophiuchus molecular clouds using large-scale c2d Spitzer surveys and Bolocam 1.1 mm continuum maps. Such a sample is critical for understanding early protostellar evolution on a statistical level, but also provides fertile ground for more detailed follow-up studies. While detailed studies have previously been carried out for a few well-know Class 0 protostars (e.g. IRAS 16293), it is not clear that such objects are representative of deeply embedded low mass protostars in general. What is the inner envelope structure of Class 0 protostars? Are relatively large (several hundred AU) holes in the inner envelope, as found for IRAS 16293, common? How does the envelope transition to a circum-protostellar disk, if present? How soon after protostar formation does such a disk form? To address these questions we have begun a study utilizing mid-infrared Spitzer IRS spectra of 25 deeply embedded protostars together with CARMA millimeter interferometric maps and radiative transfer models. IRS spectra are sensitive to the envelope optical depth near the protostar, while CARMA observations with broad uv coverage are complementary in that they can separate disk and envelope components and confirm the presence of inner envelope holes. I will discuss implications for early protostellar evolution based on the larger c2d sample, including evolutionary timescales and evidence for episodic accretion, as well as preliminary results on the detailed structure of the youngest (Class 0) protostars in Perseus, Serpens, and Ophiuchus.
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