diff --git a/zebra-chain/src/block/header.rs b/zebra-chain/src/block/header.rs
index c0b749e9a..926103789 100644
--- a/zebra-chain/src/block/header.rs
+++ b/zebra-chain/src/block/header.rs
@@ -1,8 +1,11 @@
-use super::{difficulty::CompactDifficulty, BlockHeaderHash, Error};
+use chrono::{DateTime, Duration, Utc};
+
 use crate::equihash_solution::EquihashSolution;
 use crate::merkle_tree::MerkleTreeRootHash;
 use crate::serialization::ZcashSerialize;
-use chrono::{DateTime, Duration, Utc};
+use crate::treestate::note_commitment_tree::SaplingNoteTreeRootHash;
+
+use super::{difficulty::CompactDifficulty, BlockHeaderHash, Error};
 
 /// Block header.
 ///
diff --git a/zebra-chain/src/block/serialize.rs b/zebra-chain/src/block/serialize.rs
index 1503533a6..5ed3697a2 100644
--- a/zebra-chain/src/block/serialize.rs
+++ b/zebra-chain/src/block/serialize.rs
@@ -7,6 +7,7 @@ use crate::equihash_solution::EquihashSolution;
 use crate::merkle_tree::MerkleTreeRootHash;
 use crate::serialization::ZcashDeserializeInto;
 use crate::serialization::{ReadZcashExt, SerializationError, ZcashDeserialize, ZcashSerialize};
+use crate::treestate::note_commitment_tree::SaplingNoteTreeRootHash;
 
 use super::Block;
 use super::BlockHeader;
diff --git a/zebra-chain/src/block/tests.rs b/zebra-chain/src/block/tests.rs
index 584b739e0..d491c7626 100644
--- a/zebra-chain/src/block/tests.rs
+++ b/zebra-chain/src/block/tests.rs
@@ -6,7 +6,7 @@ use crate::merkle_tree::MerkleTreeRootHash;
 use crate::serialization::{
     SerializationError, ZcashDeserialize, ZcashDeserializeInto, ZcashSerialize,
 };
-use crate::types::BlockHeight;
+use crate::treestate::note_commitment_tree::SaplingNoteTreeRootHash;
 use crate::types::LockTime;
 use crate::Network;
 use crate::{sha256d_writer::Sha256dWriter, test::generate};
diff --git a/zebra-chain/src/lib.rs b/zebra-chain/src/lib.rs
index 9b7a4920c..776849d7a 100644
--- a/zebra-chain/src/lib.rs
+++ b/zebra-chain/src/lib.rs
@@ -19,12 +19,12 @@ pub mod addresses;
 pub mod block;
 pub mod equihash_solution;
 pub mod keys;
-pub mod note_commitment_tree;
 pub mod notes;
 pub mod parameters;
 pub mod proofs;
 pub mod serialization;
 pub mod transaction;
+pub mod treestate;
 pub mod types;
 pub mod utils;
 
diff --git a/zebra-chain/src/notes/sprout.rs b/zebra-chain/src/notes/sprout.rs
index 529dcc3cb..e24b3d47c 100644
--- a/zebra-chain/src/notes/sprout.rs
+++ b/zebra-chain/src/notes/sprout.rs
@@ -95,7 +95,6 @@ pub struct NotePlaintext {
     value: Amount<NonNegative>,
     // TODO: refine type
     rho: [u8; 32],
-    // TODO: refine as jub-jub appropriate in the base field.
     note_commitment_randomness: NoteCommitmentRandomness,
     memo: Memo,
 }
diff --git a/zebra-chain/src/transaction/serialize.rs b/zebra-chain/src/transaction/serialize.rs
index e933270ce..65657a0df 100644
--- a/zebra-chain/src/transaction/serialize.rs
+++ b/zebra-chain/src/transaction/serialize.rs
@@ -331,7 +331,7 @@ impl ZcashSerialize for Spend {
 
 impl ZcashDeserialize for Spend {
     fn zcash_deserialize<R: io::Read>(mut reader: R) -> Result<Self, SerializationError> {
-        use crate::note_commitment_tree::SaplingNoteTreeRootHash;
+        use crate::treestate::note_commitment_tree::SaplingNoteTreeRootHash;
         Ok(Spend {
             cv: reader.read_32_bytes()?,
             anchor: SaplingNoteTreeRootHash(reader.read_32_bytes()?),
diff --git a/zebra-chain/src/transaction/shielded_data.rs b/zebra-chain/src/transaction/shielded_data.rs
index caf4c517f..38c5a97c6 100644
--- a/zebra-chain/src/transaction/shielded_data.rs
+++ b/zebra-chain/src/transaction/shielded_data.rs
@@ -1,9 +1,8 @@
-// XXX this name seems too long?
-use crate::note_commitment_tree::SaplingNoteTreeRootHash;
 use crate::notes::sapling;
 use crate::proofs::Groth16Proof;
 use crate::redjubjub::{self, Binding, SpendAuth};
 use crate::serde_helpers;
+use crate::treestate::note_commitment_tree::SaplingNoteTreeRootHash;
 use futures::future::Either;
 
 /// A _Spend Description_, as described in [protocol specification §7.3][ps].
diff --git a/zebra-chain/src/transaction/tests/arbitrary.rs b/zebra-chain/src/transaction/tests/arbitrary.rs
index 7145b9a5a..858c01d6f 100644
--- a/zebra-chain/src/transaction/tests/arbitrary.rs
+++ b/zebra-chain/src/transaction/tests/arbitrary.rs
@@ -1,11 +1,11 @@
 use crate::{
-    note_commitment_tree::SaplingNoteTreeRootHash,
     notes::{sapling, sprout},
     proofs::{Groth16Proof, ZkSnarkProof},
     transaction::{
         CoinbaseData, JoinSplit, JoinSplitData, OutPoint, Output, ShieldedData, Spend, Transaction,
         TransparentInput,
     },
+    treestate::note_commitment_tree::SaplingNoteTreeRootHash,
     types::{
         amount::{Amount, NonNegative},
         BlockHeight, Script,
diff --git a/zebra-chain/src/treestate.rs b/zebra-chain/src/treestate.rs
new file mode 100644
index 000000000..32a6131a2
--- /dev/null
+++ b/zebra-chain/src/treestate.rs
@@ -0,0 +1,2 @@
+pub mod note_commitment_tree;
+// mod nullifier_set;
diff --git a/zebra-chain/src/note_commitment_tree.rs b/zebra-chain/src/treestate/note_commitment_tree.rs
similarity index 100%
rename from zebra-chain/src/note_commitment_tree.rs
rename to zebra-chain/src/treestate/note_commitment_tree.rs