The crystalline fraction (Cp fraction) of silk fibroin in silk II form from the silkworm Bombyx mori is the classic example of antiparallel beta-sheet and consists mainly of Ala, Ser, and Gly. In the C-13 CP/MAS NMR spectrum, the Ala C beta, Ser C alpha, and Ser C beta peaks are asymmetric, showing the heterogeneous nature of the structure, which is shown to consist of two different packing geometries, denoted domains A and B. In this work, these peaks were resolved and assigned using 2D C-13-C-13 homonuclear correlation NMR spectra collected with different dipolar- assisted rotational resonance (DARR) mixing times. The local structure and dynamics of serine in the Cp fraction are discussed in detail. Model peptides of the Cp fraction, [3-C-13]Ser(AGSGAG)(5) with different [3-C-13]Ser labeling positions, were prepared to clarify that the individual peaks of the Ser C beta carbons come from different domains, not from different positions within a chain. The dynamics of these individual peaks were studied by measuring C-13 T-1 values, which provide information on serine side chain dynamics and thus on the formation of intermolecular hydrogen bonding through the Ser OH group. Moreover, cross peaks between domains A and B were observed in the Ala C beta DARR spectrum with a long mixing time of 400 ms, indicating a close contact between the two geometries. We conclude that the crystalline region is heterogeneous, comprising two closely associated packing geometries that form separate but small domains.