diff --git a/public/modules/dynamic/heightmap-selection.js b/public/modules/dynamic/heightmap-selection.js
index 3c1fe962d..5a4be8f81 100644
--- a/public/modules/dynamic/heightmap-selection.js
+++ b/public/modules/dynamic/heightmap-selection.js
@@ -260,7 +260,14 @@ function getName(id) {
 }
 
 function getGraph(currentGraph) {
-  const newGraph = shouldRegenerateGrid(currentGraph, seed) ? generateGrid() : structuredClone(currentGraph);
+  if (shouldRegenerateGrid(currentGraph, seed)) return generateGrid();
+
+  // Deep clone avoiding non-cloneable properties (like D3 quadtrees with functions)
+  const newGraph = JSON.parse(JSON.stringify(currentGraph));
+  // Recreate voronoi cells since JSON doesn't preserve typed arrays or circular refs
+  const {cells, vertices} = calculateVoronoi(newGraph.points, newGraph.boundary);
+  newGraph.cells = cells;
+  newGraph.vertices = vertices;
   delete newGraph.cells.h;
   return newGraph;
 }
diff --git a/src/modules/resample.ts b/src/modules/resample.ts
index a5e31c0fc..9b78fd2e0 100644
--- a/src/modules/resample.ts
+++ b/src/modules/resample.ts
@@ -13,6 +13,48 @@ import {
 import type { River } from "./river-generator";
 import type { Point } from "./voronoi";
 
+/**
+ * Deeply clones an object, omitting properties that cannot be cloned with structuredClone.
+ * D3 quadtrees store accessor functions that fail structuredClone, so they're excluded.
+ */
+const safeDeepClone = <T>(obj: T): T => {
+  if (obj === null || typeof obj !== "object") {
+    return obj;
+  }
+
+  // Handle typed arrays - slice() creates a copy with a new underlying buffer
+  if (ArrayBuffer.isView(obj) && !(obj instanceof DataView)) {
+    return (obj as any).slice() as T;
+  }
+
+  // Handle arrays
+  if (Array.isArray(obj)) {
+    return obj.map((item) => safeDeepClone(item)) as T;
+  }
+
+  // Handle objects - skip quadtree (has functions) and other non-clonable properties
+  const cloned: Record<string, unknown> = {};
+  for (const key in obj) {
+    if (!Object.prototype.hasOwnProperty.call(obj, key)) continue;
+
+    const value = (obj as Record<string, unknown>)[key];
+
+    // Skip quadtree properties (D3 quadtrees have _x and _y functions)
+    if (value && typeof value === "object" && "_x" in (value as object)) {
+      continue;
+    }
+
+    // Skip functions
+    if (typeof value === "function") {
+      continue;
+    }
+
+    cloned[key] = safeDeepClone(value);
+  }
+
+  return cloned as T;
+};
+
 declare global {
   var Resample: Resampler;
 }
@@ -495,9 +537,9 @@ class Resampler {
   process(options: ResamplerProcessOptions): void {
     const { projection, inverse, scale } = options;
     const parentMap = {
-      grid: structuredClone(grid),
-      pack: structuredClone(pack),
-      notes: structuredClone(notes),
+      grid: safeDeepClone(grid),
+      pack: safeDeepClone(pack),
+      notes: safeDeepClone(notes),
     };
     const riversData = this.saveRiversData(pack.rivers);
 
diff --git a/src/types/PackedGraph.ts b/src/types/PackedGraph.ts
index df84be863..b07ab1d86 100644
--- a/src/types/PackedGraph.ts
+++ b/src/types/PackedGraph.ts
@@ -25,7 +25,7 @@ export interface PackedGraph {
     p: [number, number][]; // cell polygon points
     b: boolean[]; // cell is on border
     h: TypedArray; // cell heights
-    q: Quadtree<[number, number, number]>; // cell quadtree index
+    q?: Quadtree<[number, number, number]>; // cell quadtree index (optional, not cloned)
     /** Terrain type */
     t: TypedArray; // cell terrain types
     r: TypedArray; // river id passing through cell